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Variable Interest Entities and Unconsolidated Investments in Power Plants (Unconsolidated VIEs) (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]    
Equity Method Investments $ 88us-gaap_EquityMethodInvestments $ 95us-gaap_EquityMethodInvestments
Greenfield [Member]    
Schedule of Equity Method Investments [Line Items]    
Equity Method Investments 69us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_GreenfieldMember		 78us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_GreenfieldMember
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_GreenfieldMember		  
Whitby [Member]    
Schedule of Equity Method Investments [Line Items]    
Equity Method Investments $ 19us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_WhitbyMember		 $ 17us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_WhitbyMember
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= cpn_WhitbyMember