2.2.0.7 false Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category (Detail) (USD $) 154 - Disclosure - Net Change in the Assets and Liabilities Measured at Fair Value on a Recurring Basis and Included in the Level 3 Fair Value Category (Detail) true false In Millions false false 1 USD false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 shares Standard http://www.xbrl.org/2003/instance shares 0 $ false 2 USD false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 shares Standard http://www.xbrl.org/2003/instance shares 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 $ false 3 USD false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 pure Standard http://www.xbrl.org/2003/instance pure 0 shares Standard http://www.xbrl.org/2003/instance shares 0 $ false 4 USD false false iso4217_USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 shares Standard http://www.xbrl.org/2003/instance shares 0 iso4217_USD_per_shares Divide http://www.xbrl.org/2003/iso4217 USD iso4217 http://www.xbrl.org/2003/instance shares 0 pure Standard http://www.xbrl.org/2003/instance pure 0 $ 5 Beginning balance 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilities d false debit instant This element represents the aggregate amount of assets and liabilities measured at fair value on a recurring basis with a... false false false false false false false false true false false periodstartlabel false 1 true true false false 32000000 32 false false false 2 true true false false 31000000 31 false false false 3 true true false false -66000000 -66 false false false 4 true true false false 99000000 99 false false false xbrli:monetaryItemType monetary This element represents the aggregate amount of assets and liabilities measured at fair value on a recurring basis with a significant amount of unobservable inputs. No authoritative reference available. false 6 Total realized and unrealized gains (losses): 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesTotalGainsLossesRealizedUnrealizedAbstract d false na duration Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Total Gains Losses... false false false false false true false false false false false false 1 false false false false 0 0 false false false 2 false false false false 0 0 false false false 3 false false false false 0 0 false false false 4 false false false false 0 0 false false false xbrli:stringItemType string Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset And Liabilities Total Gains Losses Realized Unrealized [Abstract] false 7 Included in earnings 4 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesIncludedInEarnings d false debit duration This element represents the net amount of realized and unrealized gains or (losses) included in earnings for assets and... false false false false false false false false false false false false 1 false true false false 27000000 27 false false false 2 false true false false 3000000 3 false false false 3 false true false false 40000000 40 false false false 4 false true false false -128000000 -128 false false false xbrli:monetaryItemType monetary This element represents the net amount of realized and unrealized gains or (losses) included in earnings for assets and liabilities measured at fair value on a recurring basis and included in the Level 3 fair value category. No authoritative reference available. false 8 Included in other comprehensive income (loss) 4 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesIncludedInOtherComprehensiveIncome d false debit duration This element represents the net amount of realized and unrealized gains or (losses) included in other comprehensive income... false false false false false false false false false false false false 1 false true false false -65000000 -65 false false false 2 false true false false -7000000 -7 false false false 3 false true false false 20000000 20 false false false 4 false true false false -95000000 -95 false false false xbrli:monetaryItemType monetary This element represents the net amount of realized and unrealized gains or (losses) included in other comprehensive income (loss) for assets and liabilities measured at fair value on a recurring basis and included in the Level 3 fair value category. No authoritative reference available. false 9 Included in regulatory assets/liabilities 4 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesIncludedInRegulatoryAssetsAndLiabilities d false debit duration This element represents the net amount of realized and unrealized gains or (losses) included in regulatory assets/liabilities... false false false false false false false false false false false false 1 false true false false -13000000 -13 false false false 2 false true false false -45000000 -45 false false false 3 false true false false 1000000 1 false false false 4 false true false false 10000000 10 false false false xbrli:monetaryItemType monetary This element represents the net amount of realized and unrealized gains or (losses) included in regulatory assets/liabilities for assets and liabilities measured at fair value on a recurring basis and included in the Level 3 fair value category. No authoritative reference available. false 10 Purchases, issuances and settlements 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesPurchasesSalesIssuancesAndSettlements d false debit duration This element represents the net amount of purchases, issuances and settlements for assets and liabilities measured at fair... false false false false false false false false false false false false 1 false true false false -23000000 -23 false false false 2 false true false false 5000000 5 false false false 3 false true false false -41000000 -41 false false false 4 false true false false 118000000 118 false false false xbrli:monetaryItemType monetary This element represents the net amount of purchases, issuances and settlements for assets and liabilities measured at fair value on a recurring basis and included in the Level 3 fair value category. No authoritative reference available. false 11 Transfers out of Level 3 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesLevel3TransfersOutOf d false credit duration This element represents the net amount of transfers in to or out of the Level 3 fair value category for assets and... false false false false false false false false false false true negated false 1 false true false false 25000000 25 false false false 2 false true false false 2000000 2 false false false 3 false true false false 29000000 29 false false false 4 false true false false -15000000 -15 false false false xbrli:monetaryItemType monetary This element represents the net amount of transfers in to or out of the Level 3 fair value category for assets and liabilities measured at fair value on a recurring basis. No authoritative reference available. false 12 Ending balance 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilities d false debit instant This element represents the aggregate amount of assets and liabilities measured at fair value on a recurring basis with a... false false false false false false false false false true false periodendlabel false 1 false true false false -17000000 -17 false false false 2 false true false false -11000000 -11 false false false 3 false true false false -17000000 -17 false false false 4 false true false false -11000000 -11 false false false xbrli:monetaryItemType monetary This element represents the aggregate amount of assets and liabilities measured at fair value on a recurring basis with a significant amount of unobservable inputs. No authoritative reference available. false 13 The amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains (losses) relating to assets/liabilities still held at the reporting date 3 d_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetAndLiabilitiesChangeInUnrealizedGainsAndLossesRelatedToInstrumentsHeld d false debit duration This element represents the amount of gains (losses) for the period included in earnings attributable to the change in... false false false false false false false false false false false false 1 true true false false 4000000 4 false false false 2 true true false false 7000000 7 false false false 3 true true false false -3000000 -3 false false false 4 true true false false 2000000 2 false false false xbrli:monetaryItemType monetary This element represents the amount of gains (losses) for the period included in earnings attributable to the change in unrealized gains/losses relating to assets still held at the reporting date for assets and liabilities measured at fair value on a recurring basis with a significant amount of unobservable inputs. No authoritative reference available. false 4 9 false Millions UnKnown UnKnown false true