Fair Value (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 108	$ 129
Nuclear decommissioning trusts	985	937
Other investments	99	93
Derivative Asset, Fair Value, Gross Asset	2	1
Derivative Assets	1,194	1,160
Derivative Assets, Current	110	130
Derivative Assets, Noncurrent	1,084	1,030
Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Nuclear decommissioning trusts	624	577
Other investments	58	55
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Assets	682	632
Derivative Assets, Current	0	0
Derivative Assets, Noncurrent	682	632
Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	108	129
Nuclear decommissioning trusts	361	360
Other investments	41	38
Derivative Asset, Fair Value, Gross Asset	0	0
Derivative Assets	510	527
Derivative Assets, Current	108	129
Derivative Assets, Noncurrent	402	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