1.0.0.3 true STATEMENTS OF CONSOLIDATED SHAREHOLDERS' EQUITY (USD $) In Millions false 1 $ true false false false Common Stock [Member] us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_CommonStockMember us-gaap_StatementEquityComponentsAxis explicitMember u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 u001 Standard http://www.xbrl.org/2003/instance shares xbrli 0 false 2 $ true false false false Additional Paid-in Capital [Member] us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AdditionalPaidInCapitalMember us-gaap_StatementEquityComponentsAxis explicitMember u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 3 $ true false false false Accumulated Deficit [Member] us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_RetainedEarningsMember us-gaap_StatementEquityComponentsAxis explicitMember u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 4 $ true false false false Accumulated Other Comprehensive Loss [Member] us-gaap_StatementEquityComponentsAxis xbrldi http://xbrl.org/2006/xbrldi us-gaap_AccumulatedOtherComprehensiveIncomeMember us-gaap_StatementEquityComponentsAxis explicitMember u000 Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 5 $ 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 6 Balance, beginning of year (in shares) at Dec. 31, 2006 3 us-gaap_SharesIssued us-gaap true na instant shares No definition available. false false false true false false true false false 1 false true 314000000 314 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 false false 5 false false 0 0 false false No definition available. No authoritative reference available. false 5 Balance, beginning of year at Dec. 31, 2006 3 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false true false false true false false 1 true true 3000000 3 true false 2 true true 2977000000 2977 true false 3 true true -1355000000 -1355 true false 4 false false 0 0 false false 5 false false 0 0 false false No definition available. No authoritative reference available. false 7 Cumulative effect of adoption of convertible debt pronouncement (See Note 2(o)) 3 us-gaap_CumulativeEffectOfInitialAdoptionOfNewAccountingPrinciple us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 23000000 23 true false 3 false true -18000000 -18 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 8 Cumulative effect of change in accounting principle (see Note 2(p)) 3 cnp_CumulativeEffectOfChangeInAccountingPrinciple cnp false na duration monetary Cumulative effect of adoption of EITF 06-04. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Cumulative effect of adoption of EITF 06-04. No authoritative reference available. false 9 Balance, beginning of year (as adjusted) 3 cnp_AdjustedStockholdersEquity cnp false na instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 3000000000 3000 true false 3 false true -1373000000 -1373 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 10 Issuances related to benefit and investment plans 3 us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false true 46000000 46 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 11 Issuances related to benefit and investment plans (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 2000000 2 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 12 Issuances related to convertible debt conversions 3 us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 13 Issuances related to convertible debt conversions (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 7000000 7 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 14 Issuances related to public offerings 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 15 Issuances related to public offerings (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 16 Issuances related to public offerings, net of issuance costs 3 cnp_IssuancesRelatedToPublicOfferingsNetOfIssuanceCosts cnp false credit duration monetary Value of new stock issued, net of issuance costs during the period. false false false false false false false false false 1 false false 0 0 true false 2 false true 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Value of new stock issued, net of issuance costs during the period. No authoritative reference available. false 17 Net Income 3 us-gaap_NetIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 395000000 395 true false 4 false false 0 0 true false 5 false true 395000000 395 false false No definition available. No authoritative reference available. false 18 Cumulative effect of uncertain tax positions standard 3 us-gaap_CumulativeEffectOfInitialAdoptionOfFIN48 us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 2000000 2 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 19 Common stock dividends - $0.68 per share in 2007, $0.73 per share in 2008, and $0.76 per share in 2009 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -218000000 -218 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 20 Adjustment to pension and postretirement 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -48000000 -48 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 21 Net deferred gain (loss) from cash flow hedges 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true 4000000 4 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 22 Balance, end of year at Dec. 31, 2007 3 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 3000000 3 true false 2 false true 3046000000 3046 true false 3 false true -1194000000 -1194 true false 4 false true -44000000 -44 true false 5 false true 1811000000 1811 false false No definition available. No authoritative reference available. false 23 Balance, end of year (in shares) at Dec. 31, 2007 3 us-gaap_SharesIssued us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 323000000 323 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 7 Cumulative effect of adoption of convertible debt pronouncement (See Note 2(o)) 3 us-gaap_CumulativeEffectOfInitialAdoptionOfNewAccountingPrinciple us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 8 Cumulative effect of change in accounting principle (see Note 2(p)) 3 cnp_CumulativeEffectOfChangeInAccountingPrinciple cnp false na duration monetary Cumulative effect of adoption of EITF 06-04. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -15000000 -15 true false 4 false false 0 0 true false 5 false false 0 0 false false Cumulative effect of adoption of EITF 06-04. No authoritative reference available. false 9 Balance, beginning of year (as adjusted) 3 cnp_AdjustedStockholdersEquity cnp false na instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 3046000000 3046 true false 3 false true -1209000000 -1209 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 10 Issuances related to benefit and investment plans 3 us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false true 112000000 112 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 11 Issuances related to benefit and investment plans (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 6000000 6 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 12 Issuances related to convertible debt conversions 3 us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 13 Issuances related to convertible debt conversions (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 17000000 17 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 14 Issuances related to public offerings 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 15 Issuances related to public offerings (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 16 Issuances related to public offerings, net of issuance costs 3 cnp_IssuancesRelatedToPublicOfferingsNetOfIssuanceCosts cnp false credit duration monetary Value of new stock issued, net of issuance costs during the period. false false false false false false false false false 1 false false 0 0 true false 2 false true 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Value of new stock issued, net of issuance costs during the period. No authoritative reference available. false 17 Net Income 3 us-gaap_NetIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 446000000 446 true false 4 false false 0 0 true false 5 false true 446000000 446 false false No definition available. No authoritative reference available. false 18 Cumulative effect of uncertain tax positions standard 3 us-gaap_CumulativeEffectOfInitialAdoptionOfFIN48 us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 19 Common stock dividends - $0.68 per share in 2007, $0.73 per share in 2008, and $0.76 per share in 2009 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -245000000 -245 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 20 Adjustment to pension and postretirement 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -127000000 -127 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 21 Net deferred gain (loss) from cash flow hedges 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -4000000 -4 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 22 Balance, end of year at Dec. 31, 2008 3 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 false true 3000000 3 true false 2 false true 3158000000 3158 true false 3 false true -1008000000 -1008 true false 4 false true -131000000 -131 true false 5 false true 2022000000 2022 false false No definition available. No authoritative reference available. false 23 Balance, end of year (in shares) at Dec. 31, 2008 3 us-gaap_SharesIssued us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 346000000 346 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 7 Cumulative effect of adoption of convertible debt pronouncement (See Note 2(o)) 3 us-gaap_CumulativeEffectOfInitialAdoptionOfNewAccountingPrinciple us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 8 Cumulative effect of change in accounting principle (see Note 2(p)) 3 cnp_CumulativeEffectOfChangeInAccountingPrinciple cnp false na duration monetary Cumulative effect of adoption of EITF 06-04. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Cumulative effect of adoption of EITF 06-04. No authoritative reference available. false 9 Balance, beginning of year (as adjusted) 3 cnp_AdjustedStockholdersEquity cnp false na instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false true 3158000000 3158 true false 3 false true -1008000000 -1008 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 10 Issuances related to benefit and investment plans 3 us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false true 86000000 86 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 11 Issuances related to benefit and investment plans (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 7000000 7 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 12 Issuances related to convertible debt conversions 3 us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 13 Issuances related to convertible debt conversions (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 14 Issuances related to public offerings 3 us-gaap_StockIssuedDuringPeriodValueNewIssues us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 1000000 1 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 15 Issuances related to public offerings (in shares) 4 us-gaap_StockIssuedDuringPeriodSharesNewIssues us-gaap true na duration shares No definition available. false false false false false false false false false 1 false true 38000000 38 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 16 Issuances related to public offerings, net of issuance costs 3 cnp_IssuancesRelatedToPublicOfferingsNetOfIssuanceCosts cnp false credit duration monetary Value of new stock issued, net of issuance costs during the period. false false false false false false false false false 1 false false 0 0 true false 2 false true 427000000 427 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false Value of new stock issued, net of issuance costs during the period. No authoritative reference available. false 17 Net Income 3 us-gaap_NetIncomeLoss us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 372000000 372 true false 4 false false 0 0 true false 5 false true 372000000 372 false false No definition available. No authoritative reference available. false 18 Cumulative effect of uncertain tax positions standard 3 us-gaap_CumulativeEffectOfInitialAdoptionOfFIN48 us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 19 Common stock dividends - $0.68 per share in 2007, $0.73 per share in 2008, and $0.76 per share in 2009 3 us-gaap_DividendsCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false true -276000000 -276 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 20 Adjustment to pension and postretirement 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax us-gaap true debit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -120000000 -120 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 21 Net deferred gain (loss) from cash flow hedges 3 us-gaap_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesEffectNetOfTax us-gaap true credit instant monetary No definition available. false false false false false false false false false 1 false false 0 0 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false true -4000000 -4 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false 22 Balance, end of year at Dec. 31, 2009 3 us-gaap_StockholdersEquity us-gaap true credit instant monetary No definition available. false false false true false false false true false 1 true true 4000000 4 true false 2 true true 3671000000 3671 true false 3 true true -912000000 -912 true false 4 true true -124000000 -124 true false 5 true true 2639000000 2639 false false No definition available. No authoritative reference available. false 23 Balance, end of year (in shares) at Dec. 31, 2009 3 us-gaap_SharesIssued us-gaap true na instant shares No definition available. false false false true false false false true false 1 false true 391000000 391 true false 2 false false 0 0 true false 3 false false 0 0 true false 4 false false 0 0 true false 5 false false 0 0 false false No definition available. No authoritative reference available. false false 5 53 false Millions Millions UnKnown false true