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Income Taxes (Textuals) (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Intraperiod income tax [Line Items]        
Number of States for NOL Carryforwards 22cpn_NumberofStatesforNOLCarryforwards      
Federal statutory tax expense (benefit) rate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate  
Income Tax Disclosure (Textuals) [Abstract]        
Unrecognized Tax Benefits $ 56,000,000us-gaap_UnrecognizedTaxBenefits $ 68,000,000us-gaap_UnrecognizedTaxBenefits $ 92,000,000us-gaap_UnrecognizedTaxBenefits $ 74,000,000us-gaap_UnrecognizedTaxBenefits
Unrecognized Tax Benefits that Would Impact Effective Tax Rate 13,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate      
Unrecognized Tax Benefits Resulting in Net Operating Loss Carryforward 43,000,000cpn_UnrecognizedTaxBenefitRelatedtoDeferredTaxAsset      
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued 11,000,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued 13,000,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued    
Valuation allowance 1,836,000,000us-gaap_DeferredTaxAssetsValuationAllowance 2,246,000,000us-gaap_DeferredTaxAssetsValuationAllowance    
Valuation Allowance, Deferred Tax Asset, Change in Amount 410,000,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 24,000,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount 114,000,000us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount  
Miscellaneous increase in state, Deferred Tax Assets 18,000,000cpn_MiscellaneousincreaseinstateDeferredTaxAssets      
Tax refund due to foreign dividend income treatment 10,000,000cpn_TaxRefundDueToForeignDividendIncomeTreatment      
Tax refund plus accrued interest due to foreign dividend income treatment 13,000,000cpn_TaxRefundPlusAccruedInterestDueToForeignDividendIncomeTreatment      
Accrued interest on foreign dividend refund 3,000,000cpn_AccruedInterestOnForeignDividendRefund      
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense (2,000,000)us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense (11,000,000)us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense 4,000,000us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense  
Federal [Domain]        
Income Tax Disclosure (Textuals) [Abstract]        
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost 37,000,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
/ us-gaap_IncomeTaxAuthorityAxis
= cpn_FederalDomain		 25,000,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
/ us-gaap_IncomeTaxAuthorityAxis
= cpn_FederalDomain		    
State and Local Jurisdiction [Member]        
Income Tax Disclosure (Textuals) [Abstract]        
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost 21,000,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember		 16,000,000us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost
/ us-gaap_IncomeTaxAuthorityAxis
= us-gaap_StateAndLocalJurisdictionMember		    
Expiration date 2014 through 2034 [Member]        
Income Tax Disclosure (Textuals) [Abstract]        
Deferred Tax Assets, Operating Loss Carryforwards, State and Local 4,000,000,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal
/ us-gaap_TaxPeriodAxis
= cpn_Expirationdate2015through2034Member		      
Expiration date 2026 and 2034 [Member]        
Income Tax Disclosure (Textuals) [Abstract]        
Deferred Tax Assets, Operating Loss Carryforwards, Foreign 800,000,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign
/ us-gaap_TaxPeriodAxis
= cpn_Expirationdate2026and2034Member		      
Expiration date 2023 through 2034 [Member]        
Intraperiod income tax [Line Items]        
Deferred Tax Assets, Operating Loss Carryforwards, Domestic $ 6,900,000,000us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic
/ us-gaap_TaxPeriodAxis
= cpn_Expirationdate2023through2033Member