v2.4.1.9
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]      
Balance, beginning of period $ 14us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue $ 16us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue $ 17us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Included in net income:      
Included in operating revenues 70cpn_FairValueAssetsMeasuredWithUnobservableInputsOnRecurringBasisGainLossIncludedInOperatingRevenue [1] 5cpn_FairValueAssetsMeasuredWithUnobservableInputsOnRecurringBasisGainLossIncludedInOperatingRevenue [1] 8cpn_FairValueAssetsMeasuredWithUnobservableInputsOnRecurringBasisGainLossIncludedInOperatingRevenue [1]
Included in fuel and purchased energy expense 5cpn_FairValueAssetsMeasuredwithUnobservableInputsonRecurringBasisGainLossIncludedInFuelAndPurchasedEnergyExpense [2] 0cpn_FairValueAssetsMeasuredwithUnobservableInputsonRecurringBasisGainLossIncludedInFuelAndPurchasedEnergyExpense [2] 0cpn_FairValueAssetsMeasuredwithUnobservableInputsonRecurringBasisGainLossIncludedInFuelAndPurchasedEnergyExpense [2]
Purchases, issuances and settlements:      
Purchases 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases 6us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases 3us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Issuances 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues (2)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues (1)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetIssues
Settlements (10)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements (11)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements (11)us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount 0us-gaap_FairValueLiabilitiesLevel1ToLevel2TransfersAmount 0us-gaap_FairValueLiabilitiesLevel1ToLevel2TransfersAmount 0us-gaap_FairValueLiabilitiesLevel1ToLevel2TransfersAmount
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount 0us-gaap_FairValueLiabilitiesLevel2ToLevel1TransfersAmount 0us-gaap_FairValueLiabilitiesLevel2ToLevel1TransfersAmount 0us-gaap_FairValueLiabilitiesLevel2ToLevel1TransfersAmount
Transfers into level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 [3],[4] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 [3],[4] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3 [3],[4]
Transfers out of level 3 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 [4],[5] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 [4],[5] 0us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3 [4],[5]
Balance, end of period 85us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue 14us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue 16us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 75us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss 5us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss 8us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
Assets and Liabilities with Recurring Fair Value Measurements (Textuals) [Abstract]      
Cash Equivalents Included In Cash And Cash Equivalents, Fair Value Disclosure 679cpn_CashEquivalentsIncludedInCashAndCashEquivalentsFairValueDisclosure 889cpn_CashEquivalentsIncludedInCashAndCashEquivalentsFairValueDisclosure  
Cash Equivalents Included In Restricted Cash, Fair Value Disclosure $ 217cpn_CashEquivalentsIncludedInRestrictedCashFairValueDisclosure $ 245cpn_CashEquivalentsIncludedInRestrictedCashFairValueDisclosure  
[1] For power contracts and other power-related products, included on our Consolidated Statements of Operations.
[2] For natural gas contracts, swaps and options, included on our Consolidated Statements of Operations.
[3] There were no transfers out of level 2 into level 3 for the years ended December 31, 2014, 2013 and 2012.
[4] We transfer amounts among levels of the fair value hierarchy as of the end of each period. There were no transfers into or out of level 1 during the years ended December 31, 2014, 2013 and 2012.
[5] There were no transfers out of level 3 for the years ended December 31, 2014, 2013 and 2012.