v2.4.0.8

Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2014 MWh | Dec. 31, 2013 MWh
Power [Member] |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | (57) | (29)
Natural Gas [Member] |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Energy Measure | 230 | 448
Environmental Credits [Member] |  |
Derivative [Line Items] |  |
Derivative, Nonmonetary Notional Amount, Mass | 2 | 0
Interest Rate Swap [Member] |  |
Derivative [Line Items] |  |
Derivative, Notional Amount | $ 1,500 | $ 1,527

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