Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	$ 1,016
Intangible Assets, Accumulated Amortization	314
Intangible Assets, Net	702
Future Amortization
Actual, 2012	127
Estimated, 2013	96
Estimated, 2014	83
Estimated, 2015	75
Estimated, 2016	75
Estimated, 2017	68
Estimated, Thereafter	237
NUG contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	124	[1],[2]
Intangible Assets, Accumulated Amortization	9	[1],[2]
Intangible Assets, Net	115	[1],[2]
Future Amortization
Actual, 2012	5	[1],[2]
Estimated, 2013	5	[1],[2]
Estimated, 2014	5	[1],[2]
Estimated, 2015	5	[1],[2]
Estimated, 2016	5	[1],[2]
Estimated, 2017	5	[1],[2]
Estimated, Thereafter	90	[1],[2]
OVEC
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	54	[1]
Intangible Assets, Accumulated Amortization	3	[1]
Intangible Assets, Net	51	[1]
Future Amortization
Actual, 2012	2	[1]
Estimated, 2013	2	[1]
Estimated, 2014	2	[1]
Estimated, 2015	2	[1]
Estimated, 2016	2	[1]
Estimated, 2017	2	[1]
Estimated, Thereafter	41	[1]
Coal contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	556	[1],[3]
Intangible Assets, Accumulated Amortization	145	[1],[3]
Intangible Assets, Net	411	[1],[3]
Future Amortization
Actual, 2012	55	[1],[3]
Estimated, 2013	59	[1],[3]
Estimated, 2014	58	[1],[3]
Estimated, 2015	51	[1],[3]
Estimated, 2016	51	[1],[3]
Estimated, 2017	45	[1],[3]
Estimated, Thereafter	79	[1],[3]
Coal contracts | Recorded with Regulatory Offset
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	102
Intangible Assets, Net	68
Customer Contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	146
Intangible Assets, Accumulated Amortization	36
Intangible Assets, Net	110
Future Amortization
Actual, 2012	15
Estimated, 2013	16
Estimated, 2014	17
Estimated, 2015	17
Estimated, 2016	17
Estimated, 2017	16
Estimated, Thereafter	27
Energy contracts
Intangible Assets (Textuals) [Abstract]
Intangible Assets, Gross	136	[1]
Intangible Assets, Accumulated Amortization	121	[1]
Intangible Assets, Net	15	[1]
Future Amortization
Actual, 2012	50	[1]
Estimated, 2013	14	[1]
Estimated, 2014	1	[1]
Estimated, 2015	0	[1]
Estimated, 2016	0	[1]
Estimated, 2017	0	[1]
Estimated, Thereafter	$ 0	[1]

[1] Fair value measurements of intangible assets recorded in connection with the Allegheny merger (see Note 19, Merger).

[2] NUG contracts are subject to regulatory accounting and their amortization does not impact earnings.

[3] A gross amount of $102 million ($68 million, net) of the coal contracts was recorded with a regulatory offset and the amortization does not impact earnings.