1.0.0.3 false CONDENSED STATEMENTS OF CONSOLIDATED CASH FLOWS (USD $) In Millions 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 3 Cash Flows from Operating Activities: 1 us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract 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 4 Net Income 2 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. false 5 Adjustments to reconcile net income to net cash provided by operating activities: 2 us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract 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 6 Depreciation and amortization 3 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 7 Amortization of deferred financing costs 3 us-gaap_AmortizationOfFinancingCosts us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 37000000 37 false false 2 false true 29000000 29 false false 3 false true 69000000 69 false false No definition available. No authoritative reference available. false 8 Deferred income taxes 3 us-gaap_DeferredIncomeTaxExpenseBenefit us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 269000000 269 false false 2 false true 487000000 487 false false 3 false true 0 0 false false No definition available. No authoritative reference available. false 9 Unrealized loss (gain) on marketable securities 3 us-gaap_MarketableSecuritiesUnrealizedGainLoss 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 10 Unrealized loss (gain) on indexed debt securities 3 cnp_UnrealizedLossGainOnIndexedDebtSecurities cnp false na duration monetary The increases (decreases) in the market value of indexed debt securities derivative which were included in earnings in the... 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 The increases (decreases) in the market value of indexed debt securities derivative which were included in earnings in the period. No authoritative reference available. false 11 Write-down of natural gas inventory 3 us-gaap_InventoryWriteDown us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 6000000 6 false false 2 false true 30000000 30 false false 3 false true 11000000 11 false false No definition available. No authoritative reference available. false 12 Equity in earnings of unconsolidated affiliates, net of distributions 3 us-gaap_IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions 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 -51000000 -51 false false 3 false true -13000000 -13 false false No definition available. No authoritative reference available. false 13 Changes in other assets and liabilities: 3 us-gaap_IncreaseDecreaseInOperatingCapitalAbstract 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 14 Accounts receivable and unbilled revenues, net 4 cnp_AccountsReceivableAndUnbilledRevenuesNet cnp false na duration monetary The net change during the reporting period in amount due within one year (or one business cycle) from customers for the... false false false false false false false false false 1 false true 283000000 283 false false 2 false true -82000000 -82 false false 3 false true 0 0 false false The net change during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services. AND The net change during the reporting period the amount of revenue for work performed for which the billing milestone has not occurred, net of uncollectible accounts. No authoritative reference available. false 15 Inventory 4 us-gaap_IncreaseDecreaseInInventories us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 236000000 236 false false 2 false true -109000000 -109 false false 3 false true -102000000 -102 false false No definition available. No authoritative reference available. false 16 Accounts payable 4 us-gaap_IncreaseDecreaseInAccountsPayable us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -237000000 -237 false false 2 false true 87000000 87 false false 3 false true -185000000 -185 false false No definition available. No authoritative reference available. false 17 Fuel cost over (under) recovery 4 us-gaap_IncreaseDecreaseInOverUnderEnergyRecovery us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -5000000 -5 false false 2 false true 45000000 45 false false 3 false true -93000000 -93 false false No definition available. No authoritative reference available. false 18 Non-trading derivatives, net 4 us-gaap_IncreaseDecreaseInCommodityContractAssetsAndLiabilities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 28000000 28 false false 2 false true -25000000 -25 false false 3 false true 11000000 11 false false No definition available. No authoritative reference available. false 19 Margin deposits, net 4 cnp_MarginDepositsNet cnp false na duration monetary The net change during the reporting period in money or securities placed with a broker or counterparty as security for a... false false false false false false false false false 1 false true 116000000 116 false false 2 false true -182000000 -182 false false 3 false true 65000000 65 false false The net change during the reporting period in money or securities placed with a broker or counterparty as security for a trading or derivative position, net of amounts placed with the Company by counterparties. No authoritative reference available. false 20 Interest and taxes accrued 4 cnp_InterestAndTaxesAccrued cnp false na duration monetary The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the... false false false false false false false false false 1 false true -41000000 -41 false false 2 false true -118000000 -118 false false 3 false true -33000000 -33 false false The net change during the period in the amount of cash payments due to taxing authorities for taxes that are based on the reporting entity's earnings. AND The net change during the reporting period in interest payable, which represents the amount owed to note holders, bond holders, and other parties for interest earned on loans or credit extended to the reporting entity. No authoritative reference available. false 21 Net regulatory assets and liabilities 4 us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 0 0 false false 2 false true -366000000 -366 false false 3 false true 81000000 81 false false No definition available. No authoritative reference available. false 22 Other current assets 4 cnp_NetChangeOtherCurrentAssets cnp false na duration monetary The net change during the reporting period in other current assets not otherwise defined in the taxonomy. false false false false false false false false false 1 false true 27000000 27 false false 2 false true -27000000 -27 false false 3 false true 13000000 13 false false The net change during the reporting period in other current assets not otherwise defined in the taxonomy. No authoritative reference available. false 23 Other current liabilities 4 cnp_NetChangeOtherCurrentLiabilities cnp false na duration monetary The net change during the reporting period in other current liabilities not otherwise defined in the taxonomy. false false false false false false false false false 1 false true 6000000 6 false false 2 false true 29000000 29 false false 3 false true -20000000 -20 false false The net change during the reporting period in other current liabilities not otherwise defined in the taxonomy. No authoritative reference available. false 24 Other assets 4 cnp_NetChangeOtherAssetsNoncurrent cnp false na duration monetary The net change during the reporting period in other non-current assets not otherwise defined in the taxonomy. false false false false false false false false false 1 false true -1000000 -1 false false 2 false true -20000000 -20 false false 3 false true -20000000 -20 false false The net change during the reporting period in other non-current assets not otherwise defined in the taxonomy. No authoritative reference available. false 25 Other liabilities 4 cnp_NetChangeOtherLiabilitiesNoncurrent cnp false na duration monetary The net change during the reporting period in other non-current liabiltiies not otherwise defined in the taxonomy. false false false false false false false false false 1 false true 3000000 3 false false 2 false true -8000000 -8 false false 3 false true -51000000 -51 false false The net change during the reporting period in other non-current liabiltiies not otherwise defined in the taxonomy. No authoritative reference available. false 26 Other, net 3 us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 16000000 16 false false 2 false true -33000000 -33 false false 3 false true 12000000 12 false false No definition available. No authoritative reference available. false 27 Net cash provided by operating activities 2 us-gaap_NetCashProvidedByUsedInOperatingActivities us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true 1841000000 1841 false false 2 false true 851000000 851 false false 3 false true 774000000 774 false false No definition available. No authoritative reference available. false 28 Cash Flows from Investing Activities: 1 us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract 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 29 Capital expenditures 2 us-gaap_PaymentsToAcquireProductiveAssets us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -1160000000 -1160 false false 2 false true -1020000000 -1020 false false 3 false true -1114000000 -1114 false false No definition available. No authoritative reference available. false 30 Decrease (increase) in restricted cash of transition and system restoration bond companies 2 us-gaap_IncreaseDecreaseInRestrictedCash us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 26000000 26 false false 2 false true -11000000 -11 false false 3 false true -1000000 -1 false false No definition available. No authoritative reference available. false 31 Decrease (increase) in notes receivable from unconsolidated affiliates 2 us-gaap_PaymentsForAdvanceToAffiliate us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 323000000 323 false false 2 false true -175000000 -175 false false 3 false true -148000000 -148 false false No definition available. No authoritative reference available. false 32 Investment in unconsolidated affiliates 2 us-gaap_PaymentsToAcquireInterestInJointVenture us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -115000000 -115 false false 2 false true -206000000 -206 false false 3 false true -39000000 -39 false false No definition available. No authoritative reference available. false 33 Other, net 2 us-gaap_PaymentsForProceedsFromOtherInvestingActivities us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 30000000 30 false false 2 false true 44000000 44 false false 3 false true 2000000 2 false false No definition available. No authoritative reference available. false 34 Net cash used in investing activities 2 us-gaap_NetCashProvidedByUsedInInvestingActivities us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -896000000 -896 false false 2 false true -1368000000 -1368 false false 3 false true -1300000000 -1300 false false No definition available. No authoritative reference available. false 35 Cash Flows from Financing Activities: 1 us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract 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 36 Increase (decrease) in short-term borrowings, net 2 cnp_IncreaseInShortTermBorrowingsNet cnp false na duration monetary The cash inflow from a borrowing having initial term of repayment within one year or the normal operating cycle, if longer. ... false false false false false false false false false 1 false true -98000000 -98 false false 2 false true -79000000 -79 false false 3 false true 45000000 45 false false The cash inflow from a borrowing having initial term of repayment within one year or the normal operating cycle, if longer. AND The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer. No authoritative reference available. false 37 Revolving credit facilities, net 2 cnp_LongTermRevolvingCreditFacilityNet cnp false na duration monetary The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and... false false false false false false false false false 1 false true -1441000000 -1441 false false 2 false true 1110000000 1110 false false 3 false true 331000000 331 false false The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer; and the cash outflow for the settlement of obligation drawn from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer. No authoritative reference available. false 38 Proceeds from long-term debt 2 us-gaap_ProceedsFromIssuanceOfLongTermDebt us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 1165000000 1165 false false 2 false true 1088000000 1088 false false 3 false true 900000000 900 false false No definition available. No authoritative reference available. false 39 Payments of long-term debt 2 us-gaap_RepaymentsOfLongTermDebt us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -222000000 -222 false false 2 false true -1373000000 -1373 false false 3 false true -548000000 -548 false false No definition available. No authoritative reference available. false 40 Debt issuance costs 2 us-gaap_PaymentsOfDebtIssuanceCosts us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -10000000 -10 false false 2 false true -26000000 -26 false false 3 false true -9000000 -9 false false No definition available. No authoritative reference available. false 41 Payment of common stock dividends 2 us-gaap_PaymentsOfDividendsCommonStock us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -276000000 -276 false false 2 false true -246000000 -246 false false 3 false true -218000000 -218 false false No definition available. No authoritative reference available. false 42 Proceeds from issuance of common stock, net 2 us-gaap_ProceedsFromIssuanceOfCommonStock us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 504000000 504 false false 2 false true 80000000 80 false false 3 false true 22000000 22 false false No definition available. No authoritative reference available. false 43 Other, net 2 us-gaap_ProceedsFromPaymentsForOtherFinancingActivities us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true 6000000 6 false false 2 false true 1000000 1 false false 3 false true 5000000 5 false false No definition available. No authoritative reference available. false 44 Net cash provided by (used in) financing activities 2 us-gaap_NetCashProvidedByUsedInFinancingActivities us-gaap true debit duration monetary No definition available. false false false false false false false false false 1 false true -372000000 -372 false false 2 false true 555000000 555 false false 3 false true 528000000 528 false false No definition available. No authoritative reference available. false 45 Net Increase in Cash and Cash Equivalents 1 us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease us-gaap true na duration monetary No definition available. false false false false false false false false false 1 false true 573000000 573 false false 2 false true 38000000 38 false false 3 false true 2000000 2 false false No definition available. No authoritative reference available. false 46 Cash and Cash Equivalents at Beginning of Year 1 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false true false false 1 false true 167000000 167 false false 2 false true 129000000 129 false false 3 false true 127000000 127 false false No definition available. No authoritative reference available. false 47 Cash and Cash Equivalents at End of Year 1 us-gaap_CashAndCashEquivalentsAtCarryingValue us-gaap true debit instant monetary No definition available. false false false false false false false true false 1 false true 740000000 740 false false 2 false true 167000000 167 false false 3 false true 129000000 129 false false No definition available. No authoritative reference available. false 49 Cash Payments: 2 cnp_CashPayments cnp false 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 50 Interest, net of capitalized interest 3 us-gaap_InterestPaidNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true 624000000 624 false false 2 false true 586000000 586 false false 3 false true 572000000 572 false false No definition available. No authoritative reference available. false 51 Income taxes (refunds), net 3 us-gaap_IncomeTaxesPaidNet us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 false true -9000000 -9 false false 2 false true -84000000 -84 false false 3 false true 205000000 205 false false No definition available. No authoritative reference available. false 52 Non-cash transactions: 2 cnp_NonCashTransactions cnp false 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 53 Accounts payable related to capital expenditures 3 us-gaap_CapitalExpendituresIncurredButNotYetPaid us-gaap true credit duration monetary No definition available. false false false false false false false false false 1 true true 84000000 84 false false 2 true true 96000000 96 false false 3 true true 75000000 75 false false No definition available. No authoritative reference available. false false 3 50 false Millions UnKnown UnKnown false true