1.0.0.3 false STATEMENTS OF CONSOLIDATED INCOME (USD $) In Millions, except Per Share data false 1 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 2 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 false 3 $ false false u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u002 Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares xbrli 0 2 Income Statement [Abstract] 0 us-gaap_IncomeStatementAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 3 Revenues 1 us-gaap_Revenues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 8281000000 8281 false false 2 true true 11322000000 11322 false false 3 true true 9623000000 9623 false false No definition available. No authoritative reference available. false 4 Expenses: 1 us-gaap_OperatingExpensesAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 5 Natural gas 2 us-gaap_CostOfPurchasedOilAndGas us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 4371000000 4371 false false 2 false true 7466000000 7466 false false 3 false true 5995000000 5995 false false No definition available. No authoritative reference available. false 6 Operation and maintenance 2 cnp_OperationAndMaintenance cnp false na duration monetary The amount of operating expense for the period for recurring costs associated with normal operations, including general and... false false false false false false false false false 1 false true 1664000000 1664 false false 2 false true 1502000000 1502 false false 3 false true 1440000000 1440 false false The amount of operating expense for the period for recurring costs associated with normal operations, including general and administrative expenses, and routine plant maintenance and repairs. No authoritative reference available. false 7 Depreciation and amortization 2 us-gaap_DepreciationAndAmortization us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 743000000 743 false false 2 false true 708000000 708 false false 3 false true 631000000 631 false false No definition available. No authoritative reference available. false 8 Taxes other than income taxes 2 us-gaap_TaxesExcludingIncomeAndExciseTaxes us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 379000000 379 false false 2 false true 373000000 373 false false 3 false true 372000000 372 false false No definition available. No authoritative reference available. false 9 Total 2 us-gaap_OperatingExpenses us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 7157000000 7157 false false 2 false true 10049000000 10049 false false 3 false true 8438000000 8438 false false No definition available. No authoritative reference available. true 10 Operating Income 1 us-gaap_OperatingIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 1124000000 1124 false false 2 false true 1273000000 1273 false false 3 false true 1185000000 1185 false false No definition available. No authoritative reference available. true 11 Other Income (Expense): 1 us-gaap_NonoperatingIncomeExpenseAbstract us-gaap true na duration string No definition available. false false false false false true false false false 1 false false 0 0 false false 2 false false 0 0 false false 3 false false 0 0 false false No definition available. false 12 Gain (loss) on marketable securities 2 us-gaap_MarketableSecuritiesGainLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 82000000 82 false false 2 false true -139000000 -139 false false 3 false true -114000000 -114 false false No definition available. No authoritative reference available. false 13 Gain (loss) on indexed debt securities 2 cnp_GainLossOnIndexedDebtSecurities cnp false na duration monetary Aggregate net gain (loss) on indexed debt securities derivative recognized in earnings during the period, before tax effects. false false false false false false false false false 1 false true -68000000 -68 false false 2 false true 128000000 128 false false 3 false true 111000000 111 false false Aggregate net gain (loss) on indexed debt securities derivative recognized in earnings during the period, before tax effects. No authoritative reference available. false 14 Interest and other finance charges 2 us-gaap_InterestAndDebtExpense us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -513000000 -513 false false 2 false true -468000000 -468 false false 3 false true -509000000 -509 false false No definition available. No authoritative reference available. false 15 Interest on transition and system restoration bonds 2 cnp_InterestOnTransitionAndSystemRestorationBonds cnp false na duration monetary Interest and debt related expenses associated with securitization bonds issued pursuant to financing orders by the Public... false false false false false false false false false 1 false true -131000000 -131 false false 2 false true -136000000 -136 false false 3 false true -123000000 -123 false false Interest and debt related expenses associated with securitization bonds issued pursuant to financing orders by the Public Utility Commission of Texas. No authoritative reference available. false 16 Distribution from AOL Time Warner litigation settlement 2 us-gaap_GainLossRelatedToLitigationSettlement us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 3000000 3 false false 2 false true 0 0 false false 3 false true 32000000 32 false false No definition available. No authoritative reference available. false 17 Additional distribution to ZENS holders 2 us-gaap_InterestExpenseOther us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -3000000 -3 false false 2 false true 0 0 false false 3 false true -27000000 -27 false false No definition available. No authoritative reference available. false 18 Equity in earnings of unconsolidated affiliates 2 us-gaap_IncomeLossFromEquityMethodInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 15000000 15 false false 2 false true 51000000 51 false false 3 false true 16000000 16 false false No definition available. No authoritative reference available. false 19 Other, net 2 us-gaap_OtherNonoperatingIncomeExpense us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 39000000 39 false false 2 false true 14000000 14 false false 3 false true 17000000 17 false false No definition available. No authoritative reference available. false 20 Total 2 us-gaap_NonoperatingIncomeExpense us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -576000000 -576 false false 2 false true -550000000 -550 false false 3 false true -597000000 -597 false false No definition available. No authoritative reference available. true 21 Income Before Income Taxes 1 us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 548000000 548 false false 2 false true 723000000 723 false false 3 false true 588000000 588 false false No definition available. No authoritative reference available. true 22 Income tax expense 1 us-gaap_IncomeTaxExpenseBenefit us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -176000000 -176 false false 2 false true -277000000 -277 false false 3 false true -193000000 -193 false false No definition available. No authoritative reference available. false 23 Net Income 1 us-gaap_NetIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 372000000 372 false false 2 true true 446000000 446 false false 3 true true 395000000 395 false false No definition available. No authoritative reference available. true 24 Basic Earnings Per Share 1 us-gaap_EarningsPerShareBasic us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 1.02 1.02 false false 2 true true 1.32 1.32 false false 3 true true 1.23 1.23 false false No definition available. No authoritative reference available. false 25 Diluted Earnings Per Share 1 us-gaap_EarningsPerShareDiluted us-gaap true na duration decimal No definition available. false false false false false false false false true 1 true true 1.01 1.01 false false 2 true true 1.30 1.30 false false 3 true true 1.15 1.15 false false No definition available. No authoritative reference available. false false 3 24 false Millions UnKnown Hundreds false true