Indexed Debt Securities [Abstract] Indexed Debt Securities [Abstract] Subsidiary of CenterPoint Energy Equity Holdings [Abstract] Subsidiary Of Center Point Energy Equity Holdings Abstract -- None. No documentation exists for this element. -- Subsidiary of CenterPoint Energy equity holdings [Table] Schedule of Trading Securities and Other Trading Assets [Table] Subsidiary of CenterPoint Energy equity holdings [Axis] Schedule of Trading Securities and Other Trading Assets, Major Types of Trading Securities and Assets [Axis] Subsidiary of CenterPoint Energy equity holdings [Domain] Major Equity Holdings Domain Provides names of major equity holdings of a subsidiary of CenterPoint Energy. TW Common [Member] Tw Common Member Common stock of Time Warner. TWC Common [Member] Twc Common Member Common stock of Time Warner Cable. AOL Common [Member] Aol Common Member Common stock of AOL. Schedule of Trading Securities [Line Items] Schedule of Trading Securities and Other Trading Assets [Line Items] Number of shares of common stock held by subsidiary of CenterPoint Energy (in shares) Investment In Common Stock Shares Held By Subsidiary Number of shares of common stock held by subsidiary of CenterPoint Energy as an investment. Zero Premium Exchangeable Subordinated Notes [Abstract] Zero Premium Exchangeable Subordinated Notes Abstract -- None. No documentation exists for this element. -- Issuance date of CenterPoint Energy Zero Premium Exchangeable Subordinated Notes Zero Premium Exchangeable Subordinated Notes Issuance Date Date when the zero premium exchangeable subordinated notes were issued, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.). Interest rate of CenterPoint Energy Zero Premium Exchangeable Subordinated Notes (in hundredths) Zero Premium Exchangeable Subordinated Notes Interest Rate Stated Percentage Interest rate stated in the contractual debt agreement. Due date of CenterPoint Energy Zero Premium Exchangeable Subordinated Notes Zero Premium Exchangeable Subordinated Notes Maturity Date Date when the zero premium exchangeable subordinated notes are scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.). Original principal amount of Zero Premium Exchangeable Subordinated Notes issued by CenterPoint Energy in September 1999 Zero Premium Exchangeable Subordinated Notes Face Amount The stated principal amount of the zero premium exchangeable subordinated notes at time of issuance, which may vary from the carrying amount because of unamortized premium or discount. Outstanding amount of Zero Premium Exchangeable Subordinated Notes issued by CenterpPoint Energy in September 1999 Zero Premium Exchangeable Subordinated Notes Principal Outstanding Amount of outstanding principal due under the zero premium exchangeable subordinated notes at the end of the reporting period. Percentage of market value of referenced shares of Time Warner Common each zero premium exchangeable subordinated note could be exchanged for cash (in hundredths) Subordinated Note Cash Exchangeable Percentage Of Fair Value The percentage of the fair value of the referenced TW Common shares attributable to each note and the percentage of composite fair value each note can be exchanged for cash. Referenced common shares Referenced common shares [Abstract] Referenced common shares [Abstract] The referenced shares of common stock for each zero premium exchangeable subordinated note (in shares) Number Of Shares Referenced In Exchangeable Subordinated Note Number of shares attributable to each note and referenced in determining the fair value of the cash to be exchange at behest of note holde+U32r. Stated interest rate of CenterPoint Energy Zero Premium Exchangeable Subordinated Notes (in hundredths) Target annual yield from interest and cash dividends on referenced shares before principal amount of indexed debt securities is increased or decreased (in hundredths) Target Annual Yield On Referenced Shares Before Increase Or Decrease Of Principal Amount Of Subordinated Note The target annual yield from interest and cash dividends on referenced shares, before any adjustment to increase or decrease principal amount of subordinated note is made. Outstanding amount of indexed debt securities issued by CenterPoint Energy in September 1999 Contingent principal amount of indexed debt securities issued by CenterpPoint Energy in September 1999 and outstanding and exchangeable Zero Premium Exchangeable Subordinated Notes Contingent Principal Amount Outstanding Amount of outstanding contingent principal under the zero premium exchangeable subordinated notes contract contingent principal clause. Percentage of market value of referenced shares of Time Warner Common each original indexed security note could be exchanged for cash (in hundredths) The market value of referenced shares of TW Common, TWC Common and AOL common for each indexed debt security Fair Market Value Of Referenced Shares Attributable To Zero Premium Exchangeable Subordinated Notes The market value of the referenced shares attributable to zero premium exchangeable subordinated note The cash exchange amount from referenced shares per $1,000 face amount of individual notes Subordinated Note Cash Exchange Amount Per Each Original Note The amount of cash each original principal individual note can be exchanged for a the behest of the note holder. Face amount of each indexed debt security notes issued by CenterPoint Energy in September 1999 Dollar Face Amount Of Individual Note The dollar denomination for each individual note The accretion rate for interest charges on bifurcated debt component of indexed debt securities (in hundredths) Bifurcated Debt Annual Accretion Rate The accretion rate for interest charges on bifurcated debt component of indexed debt securities (in hundredths) TW Securities Tw Securities [ Abstract] -- None. No documentation exists for this element. -- TW Securities Marketable Securities, Current Gain on TW Securities Marketable Securities, Gain (Loss) TW Securities Debt component of ZENS Debt Component Of Zens Abstract -- None. No documentation exists for this element. -- Debt Component of ZENS Indexed Debt Current -- None. No documentation exists for this element. -- Accretion of debt component of ZENS Accretion Of Debt Component Indexed Debt Securities The amount of annual balance buildup of the debt portion of indexed debt securities up to the contingent principal amount on debt component of ZENS. 2 % interest paid Interest Paid Debt Component Indexed Debt Securities The amount of stated interest paid during the current period for interest owed on debt component of ZENS. Debt Component of ZENS Derivative component of ZENS Derivative Component Of Zens Abstract -- None. No documentation exists for this element. -- Derivative Component of ZENS Indexed debt securities derivative -- None. No documentation exists for this element. -- Loss (gain) on indexed debt securities Gain (loss) on Indexed Debt Securities Gain (loss) on Indexed Debt Securities. Derivative Component of ZENS Property, Plant and Equipment [Abstract] Property, Plant and Equipment Property, Plant and Equipment Disclosure [Text Block] Income Tax Disclosure [Abstract] Current income tax expense (benefit): Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Current Federal Tax Expense (Benefit) State Current State and Local Tax Expense (Benefit) Total current expense (benefit) Current Income Tax Expense (Benefit) Deferred income tax expense (benefit): Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Federal Deferred Federal Income Tax Expense (Benefit) State Deferred State and Local Income Tax Expense (Benefit) Total deferred expense Deferred Income Tax Expense (Benefit) Total income tax expense Income Tax Expense (Benefit) Income tax reconciliation [Abstract] Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract] Income before income taxes and extraordinary item Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Federal statutory income tax rate (in hundredths) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate Expected federal income tax expense Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate Increase (decrease) in tax expense resulting from: Change In Tax Expense Abstract -- None. No documentation exists for this element. -- State income tax expense, net of federal income tax Income Tax Reconciliation, State and Local Income Taxes Amortization of investment tax credit Income Tax Reconciliation, Tax Credits, Investment Tax law change in deductibility of retiree health care costs Tax law change in deductibility of retiree health care costs The portion of the difference, between total income tax expense (benefit) as reported in the Income Statement for the period and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to tax law change in deductibility of retiree health care costs. Increase (decrease) in settled and uncertain income tax positions Income Tax Reconciliation Tax Settlements And Uncertain Income Tax Positions The sum of the differences between total income tax expense (benefit) as reported in the Income Statement and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to all income tax settlements for the period and changes in uncertain income tax positions. Other, net Income Tax Reconciliation, Other Reconciling Items Total Income Tax Reconciliation Change In Tax Expense Represents the increase (decrease) in tax expense resulting from various reconciling items. Total income tax expense Effective tax rate (in hundredths) Effective Income Tax Rate, Continuing Operations Amount of non-cash recorded to income tax expense as result of change in tax law Amount of non-cash recorded to income tax expense as result of change in tax law The increase in total income tax expense for the period as result of change in tax law. Amount of reduction to deferred tax assets due to actuarially determined net present value of lost future health care deductions Amount of reduction to deferred tax assets due to actuarially determined net present value of lost future health care deductions The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from actuarially determined net present value of lost future health care deductions, which can only be deducted for tax purposes when actual costs are incurred, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken. Amount of adjustment to regulatory assets due to actuarially determined net present value of lost future health care deductions Deferred Tax Assets, Regulatory Assets and Liabilities Amount of reduction to deferred tax assets, recorded to income tax expense, due to actuarially determined net present value of lost future health care deductions Amount of reduction to deferred tax assets, recorded to income tax expense, due to actuarially determined net present value of lost future health care deductions The amount of income tax expense recorded for the period due to actuarially determined net present value of lost future health care deductions. Amount of decrease in income tax expense recorded related to effects of re-measuring accumulated deferred income taxes Amount of decrease in income tax expense recorded related to effects of re-measuring accumulated deferred income taxes The decrease in total income tax expense for the period as a result of re-measurement of accumulated deferred income taxes associated with restructuring of company's subsidiaries. Amount of net reduction to income tax expense from state income tax expense, net of federal income tax Amount of net reduction to income tax expense from state income tax expense, net of federal income tax The component of total income tax expense for the period comprised of the net change in the entity's state income tax expense, net of federal income tax, attributable to continuing operations as determined by applying the provisions of the applicable enacted tax laws. Increase in income tax expense related to uncertain tax positions Increase in income tax expense related to uncertain tax positions Increase in income tax expense related to uncertain tax positions Income tax benefit resulting from IRS settlement Tax Adjustments, Settlements, and Unusual Provisions Reduction in the liability for uncertain tax positions Reduction In Liability For Uncertain Tax Positions Represents the reduction in the liability for uncertain tax positions. State income tax expense Benefit net of federal income tax effect related to state income tax adjustments Adjustments To Previous State Income Tax Estimates Represents adjustments to previous state income tax estimates Texas margin tax included in income tax expense State Franchise Tax Law Change Represents the impact to income tax expense from changes in state franchise taxes. Deferred tax assets: Deferred Tax Assets, Net [Abstract] Current: Deferred Tax Assets Gross Current Classification Abstract -- None. No documentation exists for this element. -- Allowance for doubtful accounts Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts Deferred gas costs Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Deferred Gas Costs The tax effect as of the balance sheet date of the amount of the estimated future tax effects attributable to the difference in fuel cost recognition for tax basis and GAAP. Other Deferred Tax Assets Current Other The tax effect as of the balance sheet date of the amount of estimated future tax deductions arising from other temporary differences not otherwise specified in the taxonomy that are expected to be resolved within 12 months of the balance sheet date. Total current deferred tax assets Deferred Tax Assets, Gross, Current Non-current: Deferred Tax Assets Gross Noncurrent Classification Abstract -- None. No documentation exists for this element. -- Loss and credit carryforwards Deferred Tax Assets Loss And Credit Tax Carryforwards The tax effect as of the balance sheet date of the amount of future tax deductions arising from loss and credit tax carryforwards and which can only be utilized if sufficient tax-basis income is generated in future periods and providing tax laws continue to allow utilization. Employee benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits Other Deferred Tax Assets Noncurrent Other The tax effect as of the balance sheet date of the amount of estimated future tax deductions arising from other temporary differences not otherwise specified in the taxonomy that are not expected to be resolved within 12 months of the balance sheet date. Total non-current deferred tax assets before valuation allowance Deferred Tax Assets, Gross, Noncurrent Valuation allowance Valuation Allowance, Amount Total non-current deferred tax assets, net of valuation allowance Deferred Tax Assets, Net, Noncurrent Total deferred tax assets, net of valuation allowance Deferred Tax Assets, Net Deferred tax liabilities: Deferred Tax Liabilities [Abstract] Current: Deferred Tax Liabilities Gross Current Classification Abstract -- None. No documentation exists for this element. -- Unrealized gain on indexed debt securities Deferred Tax Liabilities Unrealized Gains On Indexed Debt Securities The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis of indexed debt securities and the basis computed in accordance with GAAP. Unrealized gain on marketable securities Deferred Tax Liabilities Unrealized Gains On Marketable Securities The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis of marketable securities and the basis computed in accordance with GAAP. Total current deferred tax liabilities Deferred Tax Liabilities, Current Non-current: Deferred Tax Liabilities Gross Noncurrent Classification Abstract -- None. No documentation exists for this element. -- Depreciation Deferred Tax Liabilities Depreciation The amount as of the balance sheet date of the estimated future tax effects attributable to the difference between the tax basis of depreciable assets and the basis of depreciable assets computed in accordance with GAAP. The difference in basis, attributable to different depreciation methodologies, will increase future taxable income when such basis difference is realized. Depreciable assets include but are not limited to leasehold improvements, machinery and equipment and furniture and fixtures. Regulatory assets, net Deferred Tax Liabilities, Regulatory Assets and Liabilities Other Deferred Tax Liabilities Noncurrent Other The cumulative amount of the estimated future tax effects attributable to other temporary differences not otherwise specified in this taxonomy that are expected to reverse more than 12 months after the balance sheet date. Total non-current deferred tax liabilities Deferred Tax Liabilities, Noncurrent Total deferred tax liabilities Deferred Tax Liabilities Accumulated deferred income taxes, net Deferred Tax Assets (Liabilities), Net Federal net operating loss carryforwards Operating Loss Carryforwards State net operating loss carryforwards Operating Loss Carryforwards State State and local net operating loss carryforwards available to reduce future taxable income under enacted tax laws. Range of years where state net operating loss carryforwards expire. Operating Loss Carryforwards Expiration Dates State The expiration date of each operating loss carryforward included in state operating loss carryforwards, or the applicable range of such expiration dates. Valuation allowance of state capital loss carryforwards Operating Loss Carryforwards Valuation Allowance State The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from state net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized. State capital loss carryforwards Capital Loss Carryforwards State State and local net capital loss carryforwards available to reduce future taxable income under enacted tax laws. Expiration date of state capital loss carryforwards Other Tax Carryforward, Expiration Dates Balance, beginning of year Unrecognized Tax Benefits Tax Positions related to prior years: Unrecognized Tax Benefits Prior Year Tax Positions Abstract -- None. No documentation exists for this element. -- Additions Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions Reductions Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions Tax Positions related to current year: Unrecognized Tax Benefits Current Year Tax Positions Abstract -- None. No documentation exists for this element. -- Additions Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions Settlements Unrecognized Tax Benefits Resulting From Settlements With Taxing Authorities The amount of unrecognized tax benefits resulting from settlements with taxing authorities. Lapse of statute of limitations Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations Balance, end of year Reduction to liability for unrecognized tax benefits recorded Reduction to liability for unrecognized tax benefits recorded Reduction to liability for unrecognized tax benefits recorded Increase in deferred tax liability Increase in deferred tax liability Increase in deferred tax liability Decrease in income tax expense for the release of accrued interest expense Decrease in income tax expense for the release of accrued interest expense Decrease in income tax expense for the release of accrued interest expense Range of change possible in unrecognized tax benefits over the next 12 months, minimum Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Minimum For a tax position taken for which it is reasonably possible that the total amount of unrecognized tax benefit will significantly increase or decrease within twelve months of the balance sheet date, provide an estimate of the range of the reasonably possible change. This is the minimum anticipated amount. Range of change possible in unrecognized tax benefits over the next 12 months, maximum Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Maximum For a tax position taken for which it is reasonably possible that the total amount of unrecognized tax benefit will significantly increase or decrease within twelve months of the balance sheet date, provide an estimate of the range of the reasonably possible change. This is the maximum anticipated amount. Unrecognized tax benefits that, if recognized, would reduce the effective income tax rate for the year Unrecognized Tax Benefits that Would Impact Effective Tax Rate Income tax expense (benefit) recognized in interest on uncertain income tax positions during the year Unrecognized Tax Benefits, Interest on Income Taxes Expense Accrued interest on uncertain income tax positions at the end of the year Unrecognized Tax Benefits, Interest on Income Taxes Accrued Amount of Internal Revenue Service disallowance of casualty loss Amount of Internal Revenue Service disallowance of casualty loss Amount of Internal Revenue Service's disallowance of casualty loss deduction associated with damage caused by hurricane Ike. Amount of estimated liability included in taxes receivable associated with increase in income taxes Income Tax Examination, Increase (Decrease) in Liability from Prior Year Amount of indemnification receivable Amount of indemnification receivable Amount of indemnification receivable, net of tax, reflected in accounts receivable. Pertaining to the federal benefit on the deductibility of interest Federal benefit, deductibility of interest Federal benefit, deductibility of interest Other Tax Carryforward [Table] Other Tax Carryforward [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Federal [Member] Internal Revenue Service (IRS) [Member] Other Tax Carryforward Data by Item [Axis] Other Tax Carryforward Data by Item [Axis] Other Tax Carryforward, Name [Domain] Other Tax Carryforward, Name [Domain] Capital Loss Carryforward [Member] Capital Loss Carryforward [Member] Capital Loss Carryforward [Member] Charitable Contribution Carryforward [Member] Charitable Contribution Carryforward [Member] Charitable Contribution Carryforward [Member] Share Based Compensation [Member] Share Based Compensation [Member] Share Based Compensation [Member] Other Tax Carryforward [Line Items] Other Tax Carryforward [Line Items] Tax carryforward Other Tax Carryforward, Gross Amount Other tax carryforwards, expiration dates Other Tax Carryforwards Expiration Dates Other Tax Carryforwards Expiration Dates Net opearting loss carryforwards Operating Loss Carryforwards, Valuation Allowance Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] CenterPoint Energy [Member] Parent Company [Member] Long term debt [Axis] Longterm Debt Type And Discount Premium [Axis] Pertinent information about long-term debt arrangements including the carrying amount as of the balance sheet date, by type of long-term debt, including any related discount or premium information. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the company, if longer. Long term debt [Domain] Longterm Debt Type And Discount Premium Domain Type of long-term debt arrangement, such as notes, line of credit, commercial paper, asset-based financing, project financing, letter of credit financing, including any related discount or premium information. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the company, if longer. Pollution control bonds due 2015 to 2030 [Member] Bonds Pollution Control Due Range 1 [Member] Bonds Pollution Control Due Range 1 [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Repurchased Debt [Member] Repayment of Debt [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Purchased aggregate principal amount of debt Repayments of Long-term Debt Extinguishment of debt, aggregate principal amount Extinguishment of Debt, Amount Extinguishment of debt, purchase price percentage of principal (in hundredths) Extinguishment Of Debt Purchase Price Percentage Of Principal Repurchase price of debt obligations expressed as a percentage of principal amount Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum (in hundredths) Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum (in hundredths) Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum Debt Instrument, Interest Rate, Stated Percentage (in hundredths) Debt Instrument, Interest Rate, Stated Percentage Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Statement, Equity Components [Axis] Statement, Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Preference Stock [Member] Preference Stock [Member] -- None. No documentation exists for this element. -- Preferred Stock [Member] Preferred Stock [Member] Common Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Retained Earnings (Accumulated Deficit) [Member] Retained Earnings [Member] Accumulated Other Comprehensive Loss [Member] Accumulated Other Comprehensive Income (Loss) [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balance (in shares) Shares, Issued Balance Stockholders' Equity Attributable to Parent Issuance related to benefit and investment plans Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance related to benefit and investment plans (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Issuances related to public offerings Stock Issued During Period, Value, New Issues Issuances related to public offerings (in shares) Stock Issued During Period, Shares, New Issues Issuances related to public offerings, net of issuance costs Issuances Related To Public Offerings Net Of Issuance Costs Value of new stock issued, net of issuance costs during the period. Net Income Net Income (Loss) Attributable to Parent Common stock dividends Dividends, Common Stock Adjustment to pension and postretirement plans Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax Net deferred loss from cash flow hedges Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Balance (in shares) Balance Income Tax Expense Income Tax Expense Disclosure Text Block Description containing the income tax expense components. Reconciliation of Expected Federal Income Tax Expense to Actual Reconciliation Of Expected Federal Income Tax Expense To Actual Text Block A reconciliation of expected federal income tax expense using the federal statutory income tax rate to the actual income tax expense and resulting effective tax rate. Tax Assets and Liabilities Income Tax Asset Liability Disclosure Text Block Description containing the deferred asset and liability components. Rollforward of Unrecognized Tax Benefits Rollforward Of Unrecognized Tax Benefits Text Block A rollforward of the unrecognized tax benefits for the period. Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Concentration Risk [Table] Concentration Risk [Table] Concentration Risk by Benchmark [Axis] Concentration Risk by Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Workforce Subject to Collective Bargaining Arrangements [Member] Workforce Subject to Collective Bargaining Arrangements [Member] Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Concentration Risk, Percentage (in hundredths) Concentration Risk, Percentage Number of collective bargaining agreements scheduled to expire (in number of collective bargaining agreements) Number of collective bargaining agreements scheduled to expire Number of collective bargaining agreements scheduled to expire next fiscal year. Senior notes 2013 to 2041 [Member] Senior Notes Due Range 2 [Member] Senior Notes Due Range 2 [Member] Senior notes issued, due 2021 (CERC Corp senior notes) [Member] Senior Notes Issued Due 2021 Cerc Corporation Senior Notes [Member] Senior notes, due 2021, issued for extinguishment of another existing senior notes. Senior notes are notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders. Senior notes issued, due 2041 (CERC Corp senior notes) [Member] Senior Notes Issued Due 2041 Cerc Corporation Senior Notes [Member] Senior notes, due 2041, issued for extinguishment of another existing senior notes. Senior notes are notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders. Senior notes issued, due 2021 (CERC exchange offer) [Member] Senior notes issued, due 2021 (CERC exchange offer) [Member] Senior notes, due 2021, issued to replace another existing senior notes. Senior notes are notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders. Exchanged senior debt, due 2013 [Member] Exchanged Senior Debt Due 2013 [Member] Senior notes, due 2013, replaced by a newly issued senior notes. Senior notes are notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders. CERC Corp [Member] Cerc Corp Subsidiary [Member] Another company which is controlled, directly or indirectly, by its parent. The usual condition for control is ownership of a majority (over 50%) of the outstanding voting stock. The power to control may also exist with a lesser percentage of ownership, for example, by contract, lease, agreement with other stockholders or by court decree Debt refinanced Short-term Debt, Refinanced, Amount Amount of senior notes not reflected in current portion of long-term debt (CERC Corporation senior notes) Debt Instrument, Face Amount Unamortized debt issuance cost Unamortized Debt Issuance Expense Amount of cash consideration provided related to CERC exchange offer Repayments of Senior Debt Regulated Operations [Abstract] Schedule of Regulatory Assets and Liabilities [Table] Schedule Of Regulatory Assets And Liabilities [Table] A table of assets and liabilities that are created when regulatory agencies permit public utilities to defer certain costs and the recognition of certain revenues that are included in rate-setting to the balance sheet. Regulatory Assets and Liabilities [Axis] Regulatory Assets And Liabilities [Axis] The list of the regulatory assets and liabilities itemized in a table of regulatory assets and liabilities. Assets are created when regulatory agencies permits public utilities to defer costs to the balance sheet. Liabilities are created when regulatory agencies permits the public utility to defer revenue recognition to the balance sheet. These amounts would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues. Regulatory Assets and Liabilities [Domain] Regulatory Assets And Liabilities Domain The name of the regulatory asset or liability itemized in a table of regulatory assets and liabilities. Securitized regulatory asset [Member] Securitized Regulatory Asset Member Carrying value of the regulatory assets that represent capitalized stranded costs and system restoration costs that have been securitized (financed with debt). True-up Settlement [Member] True-up Settlement [Member] True-up Settlement [Member] Unrecognized equity return [Member] Unrecognized Equity Return Member Allowed return on equity that has been deferred and recorded on the balance sheet. Unamortized loss on reacquired debt [Member] Loss on Reacquired Debt [Member] Pension and rostretirement-related regulatory asset [Member] Pension And Postretirement Related Regulatory Asset [Member] Unrecognized costs associated with operations that recover pension and postretirement costs in rates and net periodic pension costs deferred according to actions of the regulator. Other long-term regulatory assets [Member] Other Longterm Regulatory Assets Member Other long-term regulatory assets that are not individually significant. Estimated removal costs [Member] Asset Retirement Obligation Costs [Member] Other long-term regulatory liabilities [Member] Other Longterm Regulatory Liabilities Member Other long-term regulatory liabilities that are not individually significant. Hurricane Ike restoration cost [Member] Storm Restoration Cost Member Represents electric transmission-related and natural gas distribution storm restoration costs that were not securitized. Schedule of Regulatory Assets and Liabilities [Line Items] Schedule Of Regulatory Assets And Liabilities [Line Items] -- None. No documentation exists for this element. -- Total regulatory assets Regulatory Assets Total regulatory liabilities Regulatory Liabilities Total regulatory assets and liabilities, net Net Regulatory Assets Amount of allowed equity return on the true-up balance that has not been recognized Unrecognized Amount Of Allowed Equity Return Amount of allowed equity return on the true-up balance that has not been recognized as it will be recognized as it is recovered in rates. Amount of allowed equity return on the true-up balance that was recognized in the period Amount Of Allowed Equity Return Recognized In Period Amount of allowed equity return on the true-up balance that was recognized in the period Amount of pension and postemployment benefits deferred as regulatory asset Amount of Pension and Postemployment Benefits Deferred as Regulatory Asset Amount of pension and postemployment benefits deferred as regulatory assets. Remaining amounts of regulatory assets for which no return on investment during recovery period is provided Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided Schedule of Property, Plant and Equipment [Table] Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment by Type [Axis] Property, Plant and Equipment by Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Electric Transmission and Distribution [Member] Electric Transmission and Distribution [Member] Natural Gas Distribution [Member] Gas Distribution Equipment [Member] Competitive Natural Gas Sales and Services [Member] Competitive Natural Gas Sales and Services [Member] Segment information for the Competitive Natural Gas Sales and Services segment which represents the non-rate regulated gas sales and services operations, which consist of three operational functions: wholesale, retail and intrastate pipelines. Interstate Pipelines [Member] Pipelines [Member] Field Services [Member] Field Services [Member] Segment information for the Field Services business segment which includes the natural gas gathering, treating and processing operations. Other property [Member] Property Plant And Equipment Other Property Member Various types of property, plant and equipment not included in other categories. Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property, Plant and Equipment, Net, by Type [Abstract] Total Property, Plant and Equipment, Gross Total accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, net Property, Plant and Equipment, Net Property, plant and equipment, useful life, weighted average (in years) Property Plant And Equipment Useful Life Weighted Average The weighted-average useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land and improvements, buildings, and production equipment. Depreciation and amortization [Abstract] Depreciation, Depletion and Amortization, Nonproduction [Abstract] Depreciation expense Depreciation, Nonproduction Amortization expense Amortization of Regulatory Asset Total depreciation and amortization expense Depreciation, Depletion and Amortization, Nonproduction Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Beginning balance Asset Retirement Obligation Accretion expense Asset Retirement Obligation, Accretion Expense Revisions in estimates of cash flows Asset Retirement Obligation, Revision of Estimate Ending balance Revisions in estimates of cash flows Asset Retirement Obligation, Period Increase (Decrease) Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Goodwill [Table] Segment Reporting Information [Axis] Statement, Business Segments [Axis] Reporting Segment [Domain] Segment [Domain] Natural Gas Distribution [Member] Natural Gas Distribution [Member] Segment information for the Natural Gas Distribution segment which consists of intrastate natural gas sales to, and natural gas transportation and distribution for, residential, commercial, industrial and institutional customers. Interstate Pipelines [Member] Interstate Pipelines [Member] Segment information for the Interstate Pipelines segment which includes the interstate natural gas pipeline operations. Field Services [Member] Other Operations [Member] Other Segment Member Segment information for the Other Operations segment which consists primarily of other corporate operations which support all of the business operations. Goodwill Reporting Information [Line Items] Goodwill Reporting Information [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Goodwill Goodwill Fair Value Disclosures [Abstract] Fair Value, Assets Measured on a Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Estimated Fair Value of Financial Instruments, Debt Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Earnings Per Share [Abstract] Basic earnings per share calculation: Earnings Per Share, Basic [Abstract] Income before extraordinary item Income (Loss) from Operations before Extraordinary Items Extraordinary Item, net of tax Extraordinary Item, Gain (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Weighted average shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Income before extraordinary item Income (Loss) from Operations before Extraordinary Items, Per Basic Share Extraordinary item, net of tax Income (Loss) from Extraordinary Items, Net of Tax, Per Basic Share Net income Earnings Per Share, Basic Diluted earnings per share calculation: Earnings Per Share, Diluted [Abstract] Net Income Plus: Incremental shares from assumed conversions: Weighted Average Number Diluted Shares Outstanding Adjustment [Abstract] Stock options (in shares) Incremental Common Shares Attributable to Share-based Payment Arrangements Restricted stock (in shares) Incremental Common Shares Attributable To Restricted Stock Restricted shares whose issuance is contingent upon certain conditions and shall be considered outstanding and included in the computation of diluted Earnings Per Share. 3.75% convertible senior notes (in shares) Incremental Common Shares Attributable To Conversion Of Senior Notes 2 Convertible Senior Notes (3.75%) outstanding shall be assumed to have been converted at the beginning of the period (or at time of issuance, if later), and the resulting common shares shall be included in common shares used to calculate diluted earnings per shares. The dilutive effect of convertible senior notes shall be reflected in diluted Earnings Per Share by application of the if-converted method. Weighted average shares assuming dilution (in shares) Weighted Average Number of Shares Outstanding, Diluted Income before extraordinary item Income (Loss) from Operations before Extraordinary Items, Per Diluted Share Extraordinary item, net of tax Income (Loss) from Extraordinary Items, Net of Tax, Per Diluted Share Net income Earnings Per Share, Diluted Outstanding shares with the options to purchase not included in the computation of diluted earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Accounting Policies [Abstract] Use of Estimates Use Of Estimates Policy Text Block Provides an entity's explanation that the preparation of financial statements in conformity with generally accepted accounting principles requires the use of management estimates. Principles of Consolidation Consolidation, Policy [Policy Text Block] Revenues Revenue Recognition, Policy [Policy Text Block] Long-lived Assets Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block] Intangibles Goodwill and Intangible Assets, Policy [Policy Text Block] Regulatory Assets and Liabilities Regulatory Assets And Liabilities Recognition Criteria Policy Text Block Describes the entity's criteria for recording regulatory assets and regulatory liabilities only because they are included in the rate-setting process, and rate-related accruals and deferrals, such as amounts receivable from (or due to) customers under fuel adjustment clauses and interim rates collected prior to regulatory approval. Depreciation and Amortization Expense Depreciation And Amortization Expense Policy Text Block Describes the methodology for allocating the cost of property, plant or equipment over the economic life of the asset in a systematic and rational manner or over a regulatory-mandated recovery period. The amortization of plant-related regulatory assets could also be described. Capitalization of Interest and Allowance for Funds Used During Construction Allowance For Funds Used During Construction Policy Text Block Describes the accounting for the Allowance for Funds Used During Construction (for example, component of Property, Plant and Equipment, credit to income statement), information regarding the inclusion in rates (only capitalized if its inclusion in rates is probable) and description of Allowance for Funds Used During Construction (for example, represents the cost of capital used during construction). Income Tax Income Tax, Policy [Policy Text Block] Accounts Receivable and Allowance for Doubtful Accounts Receivables, Policy [Policy Text Block] Inventory Inventory, Policy [Policy Text Block] Derivative Instruments Derivatives, Policy [Policy Text Block] Investments in Other Debt and Equity Securities Investment, Policy [Policy Text Block] Environmental Costs Environmental Costs, Policy [Policy Text Block] Statement of Consolidated Cash Flows Statement of Consolidated Cash Flows [Policy Text Block] Statement of Consolidated Cash Flows [Policy Text Block] Segment Reporting [Abstract] Reportable Business Segments Segment Reporting Disclosure [Text Block] Schedule of Short-term Borrowings and Long-term Debt Schedule of Debt [Table Text Block] Schedule of Revolving Credit Facilities and Utilization of Such Facilities Schedule of Line of Credit Facilities [Table Text Block] Fair Value Assets And Liabilities Measured On Recurring Basis Disclosure Items Table Fair Value Assets And Liabilities Measured On Recurring Basis Disclosure Items [Table] -- None. No documentation exists for this element. -- Fair value, assets and liabilities measured on a recurring basis [Axis] Fair Value Assets And Liabilities Measured On Recurring Basis Disclosure Items [Axis] This element represents a number of concepts which are required or desirable disclosure items concerning assets and liabilities, including [financial] instruments that are classified in stockholders' equity, which are measured at fair value on a recurring basis. Fair value, assets and liabilities measured on a recurring basis [Domain] Fair Value Assets And Liabilities Measured On Recurring Basis Disclosure Items Domain Provides the general information items required or determined to be disclosed with respect to assets and liabilities, including [financial] instruments that are classified in stockholders' equity, which are measured at fair value on a recurring basis. Quoted prices in active markets for identical assets (Level 1) [Member] Fair Value, Inputs, Level 1 [Member] Significant other observable inputs (Level 2) [Member] Fair Value, Inputs, Level 2 [Member] Significant unobservable inputs (Level 3) [Member] Fair Value, Inputs, Level 3 [Member] Netting Adjustments [Member] Netting Adjustments [Member] This item represents the amount of adjustment to assets or liabilities, due to the netting arrangements as specified in master contract. Relates to derivative contracts with counterparties. Fair Value, Assets or Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, by Asset Type [Axis] Fair Value Assets Or Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Asset Type [Axis] This element represents a number of concepts which are required or determined to be provided for purposes of reconciling beginning and ending balances of fair value measurements of assets or liabilities using significant unobservable inputs (Level 3). Fair Value, Assets or Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Asset Types [Domain] Fair Value Assets Or Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Asset Types [Domain] This element provides general categories of investment for which the fair value measurement of assets or liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period. Derivative Financial Instruments, Assets and Liabilities, Net [Member] Derivative Financial Instruments Assets And Liabilities Net Member This element represents types of derivative financial instruments which are financial instruments or other contractual arrangements with all three of the following characteristics: (a) it has (1) one or more underlying and (2) one or more notional amounts or payment provisions or both. Those terms determine the amount of the settlement or settlements, and, in some cases, whether or not a settlement is required; (b) it requires no initial net investment or an initial net investment that is smaller than would be required for other types of contracts that would be expected to have a similar response to changes in market factors; and (c) its terms require or permit net settlement, it can readily be settled net by a means outside the contract, or it provides for delivery of an asset that puts the recipient in a position not substantially different from net settlement. Notwithstanding the above characteristics, loan commitments that relate to the origination of mortgage loans that will be held for sale shall be accounted for as derivative instruments by the issuer of the loan commitment (that is, the potential lender). Fair value, by balance sheet grouping, disclosure item amounts [Axis] Fair Value, by Balance Sheet Grouping, Disclosure Item Amounts [Axis] Fair Value, Disclosure Item Amounts [Domain] Fair Value, Disclosure Item Amounts [Domain] Carrying amount [Member] Carrying (Reported) Amount, Fair Value Disclosure [Member] Fair value [Member] Estimate of Fair Value, Fair Value Disclosure [Member] Fair Value, assets and liabilities measured on recurring basis, financial statement captions Fair Value Assets And Liabilities Measured On Recurring Basis Financial Statement Captions [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Assets Assets [Abstract] Corporate equities Fair Value Assets Measured On Recurring Basis Corporate Equities This element represents a certain statement of financial position asset caption which represents a class of assets, or which may include an individual asset, measured at fair value on a recurring basis. Investments, including money market funds Investments, Fair Value Disclosure Natural gas derivatives Derivative Assets Total assets Fair Value Assets Measured On Recurring Basis Assets Total This element represents a certain statement of financial position asset caption which represents all assets, measured at fair value on a recurring basis. Liabilities Liabilities [Abstract] Indexed debt securities derivative Natural gas derivatives Derivative Financial Instruments, Liabilities, Fair Value Disclosure Total liabilities Fair Value Liabilities Measured On Recurring Basis Liabilities Total This element represents a certain statement of financial position liability caption which represents all liabilities, measured at fair value on a recurring basis. Long-term debt Long Term Debt Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents long term debt as of the balance sheet date Gain associated with price stabilization activities of CenterPoint Energy's Natural Gas Distribution business segment Gain Loss Associated With Price Stabilization Activities The aggregate net gain (loss) on derivatives associated with price stabilization activities. Cash collateral posted with counterparties Cash collateral posted with counterparties The amount of cash that is posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. Fair value measurement using significant unobservable input (level 3) reconciliation [Roll Forward] Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. Beginning balance Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Net Asset Liability Value This element represents the net asset/liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. Total unrealized gains or (losses): Total Unrealized Gains Or Losses Net Abstract -- None. No documentation exists for this element. -- Included in earnings Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Unrealized Gain Loss Included In Earnings This element represents total unrealized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value. Included in regulatory assets Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Unrealized Gain Loss Included In Regulatory Assets This element represents total unrealized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in regulatory assets. Total settlements: Purchases Sales And Other Settlements Net [Abstract] -- None. No documentation exists for this element. -- Included in earnings Included In Earnings Purchases Sales And Other Settlements Net This element represents purchases, sales, issuances, and settlements (net), included in earnings, which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3). Included in regulatory assets Included In Regulatory Assets Purchases Sales And Other Settlements Net This element represents purchases, sales, issuances, and settlements (net), included in regulatory assets, which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3). Total purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Net transfers into level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Ending balance The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date Amount Of Total Gains For Period Included In Earnings This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in assets still held at reporting period. Such unrealized (holding) gains or losses relate to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3). Zero Premium Exchangeable Subordinated Notes Maturity Date Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investment, Equity Method Investee, Name [Axis] Equity Method Investee, Name [Domain] Southeast Supply Header, LLC [Member] Southeast Supply Header Llc [Member] The equity method investment in Southeast Supply Header LLC. Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Equity method investment, ownership percentage (in hundredths) Equity Method Investment, Ownership Percentage Length of the interstate natural gas pipeline (in miles) Length Of Interstate Natural Gas Pipeline The length of pipeline, in miles, owned and operated by Southeast Supply Header, LLC. Pre-tax charges December 31, 2010 Discontinued Application of Specialized Accounting for Regulated Operations Tax Benefit Discontinued Application Of Specialized Accounting For Regulated Operations Tax Benefit The tax benefit (expense) for the discontinued application of specialized accounting for regulated operations. Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Table] Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Table] Fair value of pension and postretirement plan assets by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets or liabilities (Level 1), Significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). Pension Plan Disclosures By Plan Type [Axis] Reflects the description and required disclosures pertaining to the entity's pension plans, by plan type. Pension Plan By Plan Type Domain The name of the pension plan or a description of the plans grouped. Pension plans may grouped, for example, into pension qualified and pension non-qualified. Qualified Pension Plan [Member] Pension Plan Qualified Member A form of retirement plan that meets requirements of the Internal Revenue Code and as a result, is eligible to receive certain tax benefits. Non-qualified Pension Plan [Member] Pension Plan Non Qualified Member A form of retirement plan that does not qualify for federal income tax deduction. Schedule of Defined benefit plans disclosures [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Schedule of Defined benefit plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Pension Plan [Member] Pension Plans, Defined Benefit [Member] Postretirement Benefits [Member] Other Postretirement Benefit Plans, Defined Benefit [Member] Fair value of plan assets measurement [Axis] Defined Benefit Plan, Fair Value of Plan Assets by Measurement [Axis] Fair value of plan assets measurement [Domain] Fair Value Plan Asset Measurement [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Defined Benefit Plan by Plan Asset Categories [Axis] Defined Benefit Plan by Plan Asset Categories [Axis] Plan Asset Categories [Domain] Plan Asset Categories [Domain] Cash [Member] Cash [Member] Common Collective Trust Funds [Member] Common Collective Trust Funds Member Consists of common collective trust funds invested in equities and fixed income securities. Corporate bonds rated Investment grade or higher [Member] Corporate Debt Securities Investment Grade Or Above Member This category includes information about debt securities with an investment grade or higher rating issued by a corporate entity with a promise of repayment. High yield corporate bonds [Member] High Yield Corporate Bonds Member This category includes information about high yield debt securities issued by a corporate entity with a promise of repayment. International equities [Member] Non Us Equities Member This category includes information about ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock, convertible securities, stock rights, or stock warrants. This category includes information about equity securities issued by a foreign corporate entity. Foreign equity securities are issuances by corporations outside the reporting entity's country of domicile. U.S. equities [Member] Us Equities Member This category includes information about ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock, convertible securities, stock rights, or stock warrants. This category includes information about equity securities issued by a domestic corporate entity. Domestic equity securities are issuances from within the reporting entity's country of domicile. Cash received as collateral from securities [Member] Securities Received As Collateral Member The fair value of collateral received against securities loaned to borrowers. U.S. government back agencies bonds [Member] US Government Agencies Debt Securities [Member] U.S. treasuries [Member] US Treasury Securities [Member] Mortgage backed securities [Member] Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Asset backed securities [Member] Asset-backed Securities, Securitized Loans and Receivables [Member] Municipal bonds [Member] US States and Political Subdivisions Debt Securities [Member] Mutual funds [Member] Equity Funds [Member] International government bonds [Member] Foreign Government Debt Securities [Member] Real estate [Member] Real Estate [Member] Obligation to return cash received as collateral from securities lending [Member] Obligations To Return Securities As Collateral [ Member] The obligation to return securities received as collateral against securities loaned to borrowers. Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items] Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items] -- None. No documentation exists for this element. -- Pension plan assets, fair value Defined Benefit Plan, Fair Value of Plan Assets Percentage of investment in common collective funds allocated to fixed income securities (in hundredths) Defined Benefit Plan Common Collective Funds Percentage Of Fixed Income Securities Actual percentage of fixed income securities held in common collective fund investments. Percentage of investment in common collective funds allocated to U.S. equities (in hundredths) Defined Benefit Plan Common Collective Funds Percentage Of Us Equities Actual percentage of U.S. equity securities held in common collective fund investments. Percentage of investment in common collective funds allocated to international equities (in hundredths) Defined Benefit Plan Common Collective Funds Percentage Of International Equities Actual percentage of international equity securities held in common collective fund investments. Percentage of investment in mutual funds allocated to international equities Defined Benefit Plan Mutual Funds Percentage Of International Equities Defined Benefit Plan Mutual Funds Percentage Of International Equities Percentage of investment in mutual funds allocated to fixed income securities (in hundredths) Defined Benefit Plan Mutual Funds Percentage Of Fixed Income Securities Actual percentage of fixed income securities held in mutual fund investments. Percentage of investment in mutual funds allocated to U.S. equities (in hundredths) Defined Benefit Plan Mutual Funds Percentage Of Us Equities Actual percentage of U.S. equity securities held in mutual fund investments. Rollforward of significant unobservable inputs (level 3) plan assets [Abstract] Rollforward Of Significant Unobservable Inputs Level3 Plan Assets Abstract -- None. No documentation exists for this element. -- Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Defined Benefit Plan Change In Fair Values Of Plan Assets Roll Forward A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. Balance, beginning of year Defined Benefit Plan Fair Value Of Unobservable Plan Assets Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets. Defined Benefit Plan, Actual Return on Plan Assets Still Held Defined Benefit Plan, Actual Return on Plan Assets Still Held Unrealized losses relating to instruments still held at the reporting date Defined Benefit Plan Unrealized Losses Relating To Instruments Still At Reporting Period Gross appreciation or the gross loss in value of investments still held at the reporting date. Purchases, sales, issuances, and settlement (net) Defined Benefit Plan Purchases Sales Issuances And Settlements Purchases, sales, issuances, and settlements of investments categorized as Level 3 fair value. Transfer out of Level 3 Defined Benefit Plan Transfer Out Of Level 3 Amount of investments transferred out of Level 3 fair value category. Balance, end of year Percentage of investment in mutual funds allocated to fixed income securities under the postretirement plan (in hundredths) Postretirement Plan Mutual Funds Percentage Of Fixed Income Securities Actual percentage of fixed income securities held in mutual fund investments under the post-retirement plan. Percentage of investment in mutual funds allocated to U.S. equity securities under the postretirement plan (in hundredths) Postretirement Plan Mutual Funds Percentage Of Us Equities Actual percentage of U.S. equity securities held in mutual fund investments under the post-retirement plan. Percentage of investment in mutual funds allocated to international equity securities under the postretirement plan (in hundredths) Postretirement Plan Mutual Funds Percentage Of Us International Equities Actual percentage of international equity securities held in mutual fund investments under the post-retirement plan. Total contributions to the plans during the period Contributions made during the year, net of any cash subsidies from the government Contributions made during the year, net of any cash subsidies from the government Estimated future contributions in the next fiscal year Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year Defined Benefit Plan, Estimated Future Benefit Payments [Abstract] Defined Benefit Plan, Estimated Future Benefit Payments [Abstract] Pension benefit payments 2012 Defined Benefit Plan, Expected Future Benefit Payments in Year One Pension benefit payments 2013 Defined Benefit Plan, Expected Future Benefit Payments in Year Two Pension benefit payments 2014 Defined Benefit Plan, Expected Future Benefit Payments in Year Three Pension benefit payments 2015 Defined Benefit Plan, Expected Future Benefit Payments in Year Four Pension benefit payments 2016 Defined Benefit Plan, Expected Future Benefit Payments in Year Five Postretirement benefit payments 2017 - 2021 Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter Postretirement benefit payments 2012 Postretirement Benefit Plan Expected Future Benefit Payments In Year One The amount of postretirement benefits expected to be paid in Year 1. Postretirement benefit payments 2013 Postretirement Benefit Plan Expected Future Benefit Payments In Year Two The amount of postretirement benefits expected to be paid in Year 2. Postretirement benefit payments 2014 Postretirement Benefit Plan Expected Future Benefit Payments In Year Three The amount of postretirement benefits expected to be paid in Year 3. Postretirement benefit payments 2015 Postretirement Benefit Plan Expected Future Benefit Payments In Year Four The amount of postretirement benefits expected to be paid in Year 4. Postretirement benefit payments 2016 Postretirement Benefit Plan Expected Future Benefit Payments In Year Five The amount of postretirement benefits expected to be paid in Year 5. Postretirement benefit payments 2017 - 2021 Postretirement Benefit Plan Expected Future Benefit Payments In Five Fiscal Years Thereafter The amount of the aggregate benefits expected to be paid in the five fiscal years thereafter (the aggregate amount of postretirement benefits expected to be paid in years 6 through 10 after the date of the latest statement of financial position). Medicare subsidy receipts - 2012 Medicare Subsidy Receipts Year One Amount of Medicare subsidy receipts expected to be received in Year 1 after the balance sheet date. Medicare subsidy receipts - 2013 Medicare Subsidy Receipts Year Two Amount of Medicare subsidy receipts expected to be received in Year 2 after the balance sheet date. Medicare subsidy receipts - 2014 Medicare Subsidy Receipts Year Three Amount of Medicare subsidy receipts expected to be received in Year 3 after the balance sheet date. Medicare subsidy receipts - 2015 Medicare Subsidy Receipts Year Four Amount of Medicare subsidy receipts expected to be received in Year 4 after the balance sheet date. Medicare subsidy receipts - 2016 Medicare Subsidy Receipts Year Five Amount of Medicare subsidy receipts expected to be received in Year 5 after the balance sheet date. Medicare subsidy receipts - 2017 - 2021 Medicare Subsidy Receipts Five Fiscal Years Thereafter Aggregate amount for the next five fiscal years following the first five fiscal years (that is the aggregate of fiscal years six through ten) following the balance sheet date of Medicare subsidy receipts expected to be received. Savings Plan [Abstract] Savings Plan Abstract -- None. No documentation exists for this element. -- Maximum percentage of eligible compensation employees may contribute to the savings plan (in hundredths) Maximum Percentage Of Employee Compensation Eligible For Contribution To Savings Plan The maximum percentage of an employee's pay that is eligible for participation in the company's savings plan. Percentage of employer match under the savings plan (in hundredths) Description Of Company Match Under Savings Plan Description of the employer match under the entity's savings plan Number of Common stock held by the savings plan (in shares) Number Of Shares In Common Stock Held By Savings Plan The number of shares of the entity's common stock held by the savings plan Percentage of investment in common stocks (in hundredths) Percentage of investment in common stocks Percentage of investments held by the Savings Plan in the Entity's common stock. Savings plan benefit expense Savings Plan Benefit Expense The compensation expense recognized during the period with respect to the entity's savings plan. Postemployment Benefits [Abstract] Supplemental Unemployment Benefits [Abstract] Postemployment benefit income (expense) Postemployment Benefits Income In Period The amount of income related to postemployment benefits recognized during the period. Postemployment benefit obligations Postemployment Benefits Liability Other Non-Qualified Plans [Abstract] Other Nonqualified Plan Abstract -- None. No documentation exists for this element. -- Benefit expense related to deferred compensation plans Non Qualified Deferred Compensation Plan Benefit Expense Benefit expense recorded during the period related to deferred compensation arrangements. Other non-qualified plans benefit obligations deferred compensation Other Non Qualified Plans Benefit Obligations Deferred Compensation Other non-qualified plans, benefit obligations - deferred compensation Cumulative effect of change in accounting principle Cumulative Effect Of Change In Accounting Principle Cumulative effect of adoption of EITF 06-04. Benefit obligations related to split-dollar life insurance arrangements Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent Split Dollar Life Insurance This represents the noncurrent liability related to split-dollar life insurance arrangements within other non-qualified plans. Maximum number of times annual base salary included in severance benefits for certain officers in a change of control (in number of times) Maximum Number Of Times Annual Salary Included In Severance Benefits Maximum number of times annual base salary included in severance benefits for certain officers in a change of control (in number of times) Length of agreements including severance benefits (in years) Length Of Agreements Including Severance Benefits Length of agreements including severance benefits (in years) Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Summary of Accounting Policies [Table] Waskom Gas Processing Company [Member] Waskom Gas Processing Company [Member] Waskom Gas Processing Company [Member] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Minimum ownership interest percentage for investments recorded using the equity method (in hundredths) Minimum Ownership Interest Percentage For Investments Recorded Using Entity Method The minimum ownership interest percentage for investments recorded using the equity method. Maximum ownership interest percentage for investments recorded using the equity method (in hundredths) Maximum Ownership Interest Percentage For Investments Recorded Using Entity Method The maximum ownership interest percentage for investments recorded using the equity method. Percentage of ownership interest Length of Southeast Supply Header's interstate natural gas pipeline (in miles) Length Of Interstate Natural Gas Pipeline Owned By Affiliate1 The length of interstate natural gas pipeline owned by Southeast Supply Header, LLC. Investment during the period in Southeast Supply Header, LLC Investment During Period In Affiliate1 This element represents the investment in Southeast Supply Header, LLC during the current period. Capital distribution received during the period from Southeast Supply Header, LLC Capital Distribution Received During Period From Affiliate1 This element represents the capital distribution received during the period from Southeast Supply Header, LLC. Investment during the period in Waskom Investment During Period In Affiliate Two This element represents the investment in Waskom Gas Processing Company during the current period. Number of consolidated variable interest entities Number of consolidated variable interest entities Number of consolidated variable interest entities Amount of removal costs recognized as a component of depreciation expense recorded as a regulatory liability Removal Costs Recognized As Component Of Depreciation Expense The amount of removal costs that is recognized as a component of depreciation expense. Amount of capitalized interest and allowance for funds used during construction Capitalized Interest And Allowance For Funds Used During Construction The amount of capitalized interest and allowance for funds used during construction, which is a component of construction costs representing net cost of borrowed funds used during the period of construction. Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Provision for doubtful accounts Provision for Doubtful Accounts Minimum amount available under receivables facility Minimum Amount Available Under Receivables Facility This element represents the minimum amount available under the receivables facility. Maximum amount available under receivables facility Maximum Amount Available Under Receivables Facility This element represents the maximum amount available under the receivables facility Receivables facility size at the balance sheet date Receivables Facility Size This element represents the amount available under the receivables facility at the balance sheet date. Write-Downs of Natural Gas Inventory to Lower of Cost or Market Inventory Adjustments Materials and supplies Inventory, Raw Materials and Supplies, Net of Reserves Natural gas Energy Related Inventory, Gas Stored Underground Total inventory Inventory, Net Maximum number of months from date of purchase to maturity to be classified as cash equivalent (in months) Cash Equivalents Length Of Time To Maturity To Be Classified As Cash Equivalent This element represents the maximum number of months to maturity at date of purchase for the investment to qualify as a cash equivalent. Restricted cash accounts Restricted Cash and Cash Equivalents Amount of cash and cash equivalents that is held by transition and system restoration bond subsidiaries solely to support servicing the transition and system restoration bonds. Cash And Cash Equivalents Held To Support Servicing Transition And System Restoration Bonds Amount of cash and cash equivalents that is held by transition and system restoration bond subsidiaries solely to support servicing the transition and system restoration bonds. Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Goodwill by Reportable Segments Schedule of Goodwill [Table Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Background Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Subsequent Events [Abstract] Subsequent Event [Table] Subsequent Event [Table] Dividend Declared [Member] Dividend Declared [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Subsequent Event, Date Subsequent Event, Date Subsequent Event, Amount Subsequent Event, Amount Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Text Block] Statement, Scenario [Axis] Statement, Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Statements of Consolidated Income Income Statement [Abstract] Revenues Revenues Expenses: Operating Expenses [Abstract] Natural gas Cost of Purchased Oil and Gas Operation and maintenance Operation and maintenance The amount of operating expense for the period for recurring costs associated with normal operations including general and administrative expenses, and routine plant mainentnance and repairs. Depreciation and amortization Taxes other than income taxes Taxes, Miscellaneous Total Operating Expenses Operating Income Operating Income (Loss) Other Income (Expense): Nonoperating Income (Expense) [Abstract] Gain on marketable securities Gain (loss) on indexed debt securities Interest and other finance charges Interest and Debt Expense Interest on transition and system restoration bonds Interest on Transition and System Restoration Bonds Interest on Transition and System Restoration Bonds. Equity in earnings of unconsolidated affiliates Income (Loss) from Equity Method Investments Return on true-up balance Return on true-up balance Return on true-up balance Other, net Other Nonoperating Income (Expense) Total Nonoperating Income (Expense) Income Before Income Taxes and Extraordinary Item Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest Income tax expense Income Before Extraordinary Item Net Income Basic Earnings Per Share: Income Before Extraordinary Item (in dollars per share) Extraordinary Item, net of tax (in dollars per share) Net Income (in dollars per share) Diluted Earnings Per Share: Income Before Extraordinary Item (in dollars per share) Extraordinary Item, net of tax (in dollars per share) Net Income (in dollars per share) Dividends Declared Per Share (in dollars per share) Common Stock, Dividends, Per Share, Declared Weighted Average Shares Outstanding, Basic (in shares) Weighted Average Shares Outstanding, Diluted (in shares) Short-term Borrowings and Long-term Debt Debt Disclosure [Text Block] Statements of Consolidated Comprehensive Income Statement of Income and Comprehensive Income [Abstract] Other comprehensive income (loss): Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Adjustment to pension and other postretirment plans (net of tax of $2, $5, and $7) Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Reclassification of deferred loss from cash flow hedges realized in net income (net of tax of $-0-, $-0- and $-0-) Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Pension plans by plan type [Axis] Pension plans by plan type [Domain] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Pension and Postretirement Benefits [Abstract] Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract] New percentage of eligible earnings used to determine retirement benefits (in hundredths) Defined Benefit Plan Retirement Benefit Eligible Earnings Increased Percentage The increased percentage of earnings, effective January 1, 2009, used in the cash balance formula to determine a participant's retirement benefit. Old percentage of eligible earnings used to determine retirement benefits (in hundredths) Defined Benefit Plan Retirement Benefit Eligible Earnings Previous Percentage The previous percentage of earnings, prior to January 1, 2009, used in the cash balance formula to determine a participant's retirement benefit. Percent vested Defined Benefit Plan Percentage Vested Represents the percentage vested after three years. Pension plan minimum vesting period (in years) Defined Benefit Pension Plan Vesting Period Description of the period of time after which plan participants become fully vested and are entitled to receive benefits under the non-contributory qualified defined benefit pension plan. Approximate amortization period of transition obligation (in years) Defined Benefit Plan Transition Obligation Amortization Period The period of time over which the transition obligation, resulting from future healthcare cost accruals, will be amortized. Components of net periodic costs [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Amortization of net loss Defined Benefit Plan, Amortization of Gains (Losses) Amortization of transition obligation Defined Benefit Plan, Amortization of Transition Obligations (Assets) Benefit enhancement Defined Benefit Plan Enhancements The amount of increase or decrease to net periodic benefit cost as a result of plan enhancements. Net periodic cost Defined Benefit Plan, Net Periodic Benefit Cost Assumptions used to determine net periodic benefit (income) cost Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract] Discount rate (in hundredths) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Expected return on plan assets (in hundredths) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Rate of increase in compensation levels (in hundredths) Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase Change in benefit obligation [Roll Forward] Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Benefit obligation at beginning of year Defined Benefit Plan, Benefit Obligation Service Cost Defined Benefit Plan Change in Benefit Obligations Service Cost Changes in the benefit obligation liability account for defined benefit plans due to service cost. Interest Cost Defined Benefit Plan Change in Benefit Obligation Interest Cost Changes in the benefit obligation liability account for defined benefit plans due to interest cost. Participant contributions Defined Benefit Plan, Contributions by Plan Participants Benefits paid Defined Benefit Plan, Benefits Paid Actuarial loss Defined Benefit Plan, Actuarial Net (Gains) Losses Early retiree reinsurance program reimbursement Defined Benefit Plan, Early retiree reinsurance reimbursement Defined Benefit Plan, Early retiree reinsurance reimbursement Plan amendments Defined Benefit Plan, Plan Amendments Medicare reimbursement Defined Benefit Plan, Gross Prescription Drug Subsidy Receipts Received Benefit obligation at end of year Change in plan assets [Rollforward] Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Fair value of plan assets at beginning of year Employer contributions Defined Benefit Plan, Contributions by Employer Actual investment return Defined Benefit Plan, Actual Return on Plan Assets Fair value of plan assets at end of year Funded status of plan Defined Benefit Plan, Funded Status of Plan [Abstract] Funded status at end of year Defined Benefit Plan, Funded Status of Plan Amounts recognized in balance sheets Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract] Current liabilities - other Pension and Other Postretirement Defined Benefit Plans, Current Liabilities Other liabilities-benefit obligations Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Net liability, end of year Pension and Other Postretirement Defined Benefit Plans, Liabilities Actuarial Assumptions [Abstract] Defined Benefit Plan Actuarial Assumptions Abstract -- None. No documentation exists for this element. -- Discount rate (in hundredths) Defined Benefit Plan Actuarial Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate The interest rate assumption used to adjust for the time value of money. Expected return on plan assets (in hundredths) Defined Benefit Plan Actuarial Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets An assumption pertaining to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation. Rate of increase in compensation levels (in hundredths) Defined Benefit Plan Actuarial Assumptions Used Calculating Net Periodic Benefit Cost Rate Of Compensation Increase An assumption as to the expected rate of compensation increases (for pay-related plans). Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract] Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract] Health care costs trend rate assumed for next year (in hundredths) Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year Healthcare and prescription drug cost trend rate assumed for next year (in hundredths) Defined Benefit Plan Prescription Drug Cost Trend Rate Assumed For Next Fiscal Year The assumed prescription drug cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of prescription drugs currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (in hundredths) Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Year that healthcare rate reaches the ultimate trend rate Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate Year that prescription drug rate reaches the ultimate trend rate Defined Benefit Plan Year That Prescription Drug Rate Reaches Ultimate Trend Rate Defined Benefit Plan Year That Prescription Drug Rate Reaches Ultimate Trend Rate Prescription drug cost trend rate assumed for 2013 (in hundreths) Defined Benefit Plan Healthcare and Prescription Drug Cost Trend Rate Assumed For Year Two The assumed healthcare and prescription drug cost trend rate for 2013. Accumulated benefit obligation for all defined benefit pension plans Defined Benefit Plan, Accumulated Benefit Obligation Annualized individual discount rates based on time period, minimum Annualized individual discount rates based on time period, minimum Annualized individual discount rates based on time period, minimum Annualized individual discount rates based on time period, maximum Annualized individual discount rates based on time period, maximum Annualized individual discount rates based on time period, maximum Amounts recognized in accumulated other comprehensive loss Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract] Unrecognized actuarial loss Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax Unrecognized prior service cost Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax Unrecognized transition obligation Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Transition Assets (Obligations), before Tax Net amount recognized in accumulated other comprehensive loss Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax Changes in plan assets and benefit obligations recognized in other comprehensive income Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract] Net loss Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax Amortization of net loss Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax Prior service credit Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Arising During Period, before Tax Amortization of prior service credit Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax Transition obligation Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Transition Asset (Obligation), Recognized in Net Periodic Benefit Cost, before Tax Total recognized in comprehensive income Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Tax Total expense recognized in net periodic cost and other comprehensive income Defined Benefit Plan Expense Recognized In Net Periodic Cost And Other Comprehensive Income Before Tax The total expense recognized in net periodic benefit cost and other comprehensive income for defined benefit plans for the period. Amounts that will be amortized from accumulated other comprehensive loss in next fiscal year Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract] Unrecognized actuarial loss Defined Benefit Plan, Amortization of Net Gains (Losses) Unrecognized prior service cost Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit) Amounts in comprehensive income to be recognized in net periodic cost in 2012 Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year Pension benefits that have accumulated benefit obligations in excess of plan assets Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract] Accumulated benefit obligation Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation Projected benefit obligation Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit Obligation Fair value of plan assets Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets Percentage change in the assumed healthcare cost trend rate (in hundredths) Defined Benefit Plan Health Care Cost Trend Rate Assumed Percentage Change The percentage change in the assumed health care cost trend rate. Effect of a one-percentage point change in assumed health care cost trend rates Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract] Effect of a one-percentage point increase on total service and interest cost Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components Effect of a one-percentage point decrease on total service and interest cost Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components Effect of a one-percentage point increase on post-retirement benefit obligation Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation Effect of a one-percentage point decrease on post-retirement benefit obligation Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation Weighted average target allocations Defined Benefit Plan, Assets, Target Allocations [Abstract] Domestic equity securities, minimum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Domestic Equity Securities Range Minimum Target allocation minimum percentage of investments in domestic equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. Domestic equity securities, maximum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Domestic Equity Securities Range Maximum Target allocation maximum percentage of investments in domestic equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. Global equity securities, minimum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Global Equity Securities Range Minimum Target allocation minimum percentage of investments in global equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. Global equity securities, maximum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Global Equity Securities Range Maximum Target allocation maximum percentage of investments in global equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. International equity securities, minimum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets International Equity Securities Range Minimum Target allocation minimum percentage of investments in international equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. International equity securities, maximum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets International Equity Securities Range Maximum Target allocation maximum percentage of investments in international equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position. Emerging market equity securities, minimum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Emerging Markets Equity Securities Range Minimum Defined Benefit Plan Target Allocation Percentage Of Assets Emerging Markets Equity Securities Range Minimum Emerging market equity securities, maximum (in hundredths) Defined Benefit Plan Target Allocation Percentage Of Assets Emerging Markets Equity Securities Range Maximum Defined Benefit Plan Target Allocation Percentage Of Assets Emerging Markets Equity Securities Range Maximum Debt securities, minimum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities, Range Minimum Debt securities, maximum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities, Range Maximum Real Estate, minimum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Real Estate, Range Minimum Real Estate, maximum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Real Estate, Range Maximum Cash, minimum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Other, Range Minimum Cash, maximum (in hundredths) Defined Benefit Plan, Target Allocation Percentage of Assets, Other, Range Maximum Condensed Financial Information of Parent Company Only Disclosure [Abstract] Schedule of Condensed Financial Statements [Table] Schedule of Condensed Financial Statements [Table] Legal entity [Axis] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Operation and Maintenance Expenses Total Interest Income from Subsidiaries Interest Income From Subsidiaries Interest income earned on receivables from subsidiaries and eliminated in consolidation. Other Expense Gain (Loss) on Indexed Debt Securities Interest Expense to Subsidiaries Interest Expense To Subsidiaries Interest expense for debt owed to subsidiaries and eliminated in consolidation. Interest Expense Loss Before Income Taxes, Equity in Subsidiaries and Extraordinary Item Income Tax Benefit Loss Before Equity in Subsidiaries and Extraordinary Item Income Loss Before Equity In Subsidiaries Income (loss) before earnings of subsidiaries. Equity Income of Subsidiaries Equity Income Of Subsidiaries Equity income portion from subsidiaries. Extraordinary Item, Net of Tax Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis] Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis] Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Report Line [Domain] Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Report Line [Domain] Operation And Maintenance Expense Member Operation And Maintenance Expense Member Amount of share-based compensation cost reported in the period, allocated to operations and maintenance expense. Operations and maintenance expense are the costs associated with normal operations, including general and administrative expenses, and routine plant maintenance and repairs. Inventory or Fixed Assets [Member] Inventory or Fixed Assets [Member] Inventory or Fixed Assets [Member] Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Award Type and Plan Name [Axis] Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Award Type and Plan Name [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Stock Options [Member] Performance Awards [Member] Performance Awards Member Performance awards within the entity's long-term stock incentive plan. Stock Awards [Member] Stock Awards Member Stock awards within the entity's long-term stock incentive plan. Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Shares authorized for issuance under long-term incentive plans (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Employee Service Share-based Compensation, Aggregate Disclosures [Abstract] Employee Service Share-based Compensation, Aggregate Disclosures [Abstract] LTIP compensation expense Allocated Share-based Compensation Expense Income tax benefit recognized related to LTIPs Employee Service Share-based Compensation, Tax Benefit from Compensation Expense Actual tax benefit realized for tax deductions related to LTIPs Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options Vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Dividends declared during the vesting period (in dollars per share) Minimum Total Common Stock Dividends Declared During Three Year Vesting Period Represents the minimum total common stock dividend that must be declared during the three year vesting period for stock awards Stock options vesting rights Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights Stock options contractual term Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date Summary of changes in shares outstanding under all long-term incentive plans [Rollforward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Changes in shares outstanding under all long-term incentive plans, additional disclosures [Abstract] Changes In Shares Outstanding Under Long Term Incentive Plans Additional Disclosures Abstract -- None. No documentation exists for this element. -- Number of options outstanding, beginning balance (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Number of options expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period Number of options cancelled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period Number of options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Number of options outstanding, ending balance (in shares) Number of exercisable options (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Weighted average exercise price per option, outstanding, beginning of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Weighted average exercise price per option expired (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price Weighted average exercise price per option cancelled (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Weighted average exercise price per option exercised (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Weighted average exercise price per option, outstanding, end of period (in dollars per share) Weighted average exercise price per exercisable option (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Remaining average contractual life of options outstanding (in years) Share Based Compensation Arrangement By Share Based Payment Award Options Weighted Average Remaining Contractual Term Outstanding The weighted average period between the balance-sheet date and expiration for all awards outstanding under the plan, which may be expressed in a decimal value for number of years. Remaining average contractual life of exercisable options (in years) Share Based Compensation Arrangement By Share Based Payment Award Options Weighted Average Remaining Contractual Term Exercisable The weighted average period between the balance-sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years. Aggregate intrinsic value of options outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Aggregate intrinsic value of exercisable options Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value Cash received from options exercised Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options Summary of nonvested shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward] Nonvested, beginning of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Forfeited or cancelled (in shares) Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Or Cancellations In Period