Fair Value Measurements (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Energy-related derivatives	$ 14	$ 10
Interest rate derivatives	13	10
Foreign currency derivatives	2	3
Cash equivalents and restricted cash	1,024	351
Other	67	79
Fair value assets, total	2,325	1,823
Liabilities:
Energy-related derivatives	245	206
Interest rate derivatives	33	1
Foreign currency derivatives	3
Fair value liabilities, total	281	207
Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	454	664
Foreign Equity [Member]
Assets:
Nuclear decommissioning trusts	172
U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	50	240
Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	82	53
Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	260	220
Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	151	119
Other investments [Member]
Assets:
Nuclear decommissioning trusts	36	74
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Energy-related derivatives	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0	0
Cash equivalents and restricted cash	1,024	351
Other	3	9
Fair value assets, total	1,564	984
Liabilities:
Energy-related derivatives	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0
Fair value liabilities, total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	396	604
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign Equity [Member]
Assets:
Nuclear decommissioning trusts	124
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	17	20
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Energy-related derivatives	14	10
Interest rate derivatives	13	10
Foreign currency derivatives	2	3
Cash equivalents and restricted cash	0	0
Other	50	51
Fair value assets, total	747	820
Liabilities:
Energy-related derivatives	245	206
Interest rate derivatives	33	1
Foreign currency derivatives	3
Fair value liabilities, total	281	207
Significant Other Observable Inputs (Level 2) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	58	60
Significant Other Observable Inputs (Level 2) [Member] | Foreign Equity [Member]
Assets:
Nuclear decommissioning trusts	48
Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	33	220
Significant Other Observable Inputs (Level 2) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	82	53
Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	260	220
Significant Other Observable Inputs (Level 2) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	151	119
Significant Other Observable Inputs (Level 2) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	36	74
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Energy-related derivatives	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0	0
Cash equivalents and restricted cash	0	0
Other	14	19
Fair value assets, total	14	19
Liabilities:
Energy-related derivatives	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0
Fair value liabilities, total	0	0
Significant Unobservable Inputs (Level 3) [Member] | Domestic Equity [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Unobservable Inputs (Level 3) [Member] | Foreign Equity [Member]
Assets:
Nuclear decommissioning trusts	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury and government agency securities [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Unobservable Inputs (Level 3) [Member] | Municipal bonds [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Unobservable Inputs (Level 3) [Member] | Mortgage and asset backed securities [Member]
Assets:
Nuclear decommissioning trusts	0	0
Significant Unobservable Inputs (Level 3) [Member] | Other investments [Member]
Assets:
Nuclear decommissioning trusts	$ 0	$ 0