v2.4.1.9

Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015 MWh	Dec. 31, 2014 MWh
Power [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	(79)us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = cpn_PowerMember	(62)us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = cpn_PowerMember
Natural Gas [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure	693us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_NaturalGasReservesMember	291us-gaap_DerivativeNonmonetaryNotionalAmountEnergyMeasure / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_NaturalGasReservesMember
Environmental Credits [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass	1us-gaap_DerivativeNonmonetaryNotionalAmountMass / us-gaap_DerivativeInstrumentRiskAxis = cpn_EnvironmentalCreditsMember	0us-gaap_DerivativeNonmonetaryNotionalAmountMass / us-gaap_DerivativeInstrumentRiskAxis = cpn_EnvironmentalCreditsMember
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,419invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember	1,431invest_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

- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountMass
Namespace Prefix:	us-gaap_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

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: