Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	$ 974
Intangible Assets, Accumulated Amortization	171
Intangible Assets, Net	803
Future Amortization
Actual, 2011	144
Estimated, 2012	126
Estimated, 2013	90
Estimated, 2014	77
Estimated, 2015	69
Estimated, 2016	69
Estimated, Thereafter	288
Non Utility Generation Contract
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	124
Intangible Assets, Accumulated Amortization	4
Intangible Assets, Net	120
Future Amortization
Actual, 2011	4
Estimated, 2012	5
Estimated, 2013	5
Estimated, 2014	5
Estimated, 2015	5
Estimated, 2016	5
Estimated, Thereafter	95
OVEC
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	54
Intangible Assets, Accumulated Amortization	1
Intangible Assets, Net	53
Future Amortization
Actual, 2011	1
Estimated, 2012	2
Estimated, 2013	2
Estimated, 2014	2
Estimated, 2015	2
Estimated, 2016	2
Estimated, Thereafter	43
Coal contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	516
Intangible Assets, Accumulated Amortization	74
Intangible Assets, Net	442
Future Amortization
Actual, 2011	56
Estimated, 2012	55
Estimated, 2013	53
Estimated, 2014	52
Estimated, 2015	45
Estimated, 2016	45
Estimated, Thereafter	108
Coal contracts | Recorded with Regulatory Offset
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	102
Intangible Assets, Accumulated Amortization	18
Intangible Assets, Net	84
Customer Contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	144
Intangible Assets, Accumulated Amortization	21
Intangible Assets, Net	123
Future Amortization
Actual, 2011	12
Estimated, 2012	14
Estimated, 2013	16
Estimated, 2014	17
Estimated, 2015	17
Estimated, 2016	17
Estimated, Thereafter	42
Energy contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	136
Intangible Assets, Accumulated Amortization	71
Intangible Assets, Net	65
Future Amortization
Actual, 2011	71
Estimated, 2012	50
Estimated, 2013	14
Estimated, 2014	1
Estimated, 2015	0
Estimated, 2016	0
Estimated, Thereafter	$ 0