v2.4.1.9

Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 MWh	Dec. 31, 2013 MWh
Power [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	(62)us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = cpn_PowerMember	(29)us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = cpn_PowerMember
Natural Gas [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	291us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_NaturalGasReservesMember	448us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_NaturalGasReservesMember
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,431invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember	1,527invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure
Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cpn_PowerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: