Fair Value (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 63	$ 129
Nuclear decommissioning trusts	1,029	937
Other investments	104	93
Derivative Asset, Fair Value, Gross Asset	2	1
Derivative Assets	1,198	1,160
Derivative Assets, Current	65	130
Derivative Assets, Noncurrent	1,133	1,030
Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Nuclear decommissioning trusts	651	577
Other investments	62	55
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Assets	713	632
Derivative Assets, Current	0	0
Derivative Assets, Noncurrent	713	632
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	63	129
Nuclear decommissioning trusts	378	360
Other investments	42	38
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Assets	483	527
Derivative Assets, Current	63	129
Derivative Assets, Noncurrent	420	398
Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative Asset, Fair Value, Gross Asset	2	1
Derivative Assets	2	1
Derivative Assets, Current	2	1
Derivative Assets, Noncurrent	$ 0	$ 0