Name:	cnp_AccretionOfDebtComponentIndexedDebtSecurities
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No definition available.

Name:	cnp_DebtComponentOfZensAbstract
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Amount of outstanding contingent principal under the zero premium exchangeable subordinated notes contract contingent principal clause.

No definition available.

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Period Type:	instant

No definition available.

Name:	cnp_DerivativeComponentOfZensAbstract
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This represents a distribution of cash to ZENS holders during the period in accordance with the terms of the ZENS.

No definition available.

Name:	cnp_DistributionToZENSHolders
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Data Type:	xbrli:monetaryItemType
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The dollar denomination for each individual note

No definition available.

Name:	cnp_DollarFaceAmountOfIndividualNote
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Data Type:	xbrli:monetaryItemType
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This item represents the net total realized and unrealized gain (loss) included in earnings for the period related to indexed debt securities.

No definition available.

Name:	cnp_GainLossOnIndexedDebtSecurities
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No definition available.

Name:	cnp_IndexedDebtCurrent
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No definition available.

Name:	cnp_IndexedDebtSecuritiesDerivative
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The amount of stated interest paid during the current period for interest owed on debt component of ZENS.

No definition available.

Name:	cnp_InterestPaidDebtComponentIndexedDebtSecurities
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Number of shares attributable to each note and referenced in determining the fair value of the cash to be exchange at behest of note holder.

No definition available.

Name:	cnp_NumberOfSharesReferencedInExchangeableSubordinatedNote
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Data Type:	xbrli:decimalItemType
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The amount of cash each $1,000 original principal amount of ZENS can be exchanged for a the behest of the note holder.

No definition available.

Name:	cnp_SubordinatedNoteCashExchangeAmountPerEach1000OfOriginalNote
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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.

No definition available.

Name:	cnp_SubordinatedNoteCashExchangeablePercentageOfFairValue
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Data Type:	num:percentItemType
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The target annual yield from interest and cash dividends on reference shares, before any adjustment to increase or decrease principal amount of subordinated note is made.

No definition available.

Name:	cnp_TargetAnnualYieldOnReferenceShares
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Data Type:	num:percentItemType
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No definition available.

Name:	cnp_TwSecuritiesAbstract
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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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Name:	us-gaap_DebtInstrumentFaceAmount
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Contractual interest rate for funds borrowed, under the debt agreement.

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Balance held at close of period in number of shares.

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Amount of investment in marketable security, classified as current.

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Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

No definition available.

Name:	us-gaap_MarketableSecuritiesGainLoss
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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

No definition available.

Name:	us-gaap_ProceedsFromSaleAndMaturityOfMarketableSecurities
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Data Type:	xbrli:monetaryItemType
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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.

No definition available.

Name:	us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix:	us-gaap_
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Name:	us-gaap_FinancialInstrumentAxis=cnp_ATTCommonMember
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Name:	us-gaap_FinancialInstrumentAxis=cnp_TWSecuritiesMember
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Data Type:	na
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