Fair Value (Assets and Liabilities Recorded at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets [Abstract]
Nuclear decommissioning trusts	$ 1,195	$ 1,191
Liabilities [Abstract]
Derivative Liabilities, Current	(140)	(195)
Derivative Liabilities, Noncurrent	(16)	(43)
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Cash and Cash Equivalents	58	125
Nuclear decommissioning trusts	1,195	1,191
Other investments	138	136
Derivative assets [Abstract]
Derivative Assets	96	126
Assets, Fair Value Disclosure	1,487	1,578
Liabilities [Abstract]
Derivative Liabilities	(156)	(238)
Fair Value, Net Asset (Liability)	1,331	1,340
Derivative Liabilities, Current	(140)	(195)
Derivative Liabilities, Noncurrent	(16)	(43)
Fair Value, Measurements, Recurring [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	16	14
Liabilities [Abstract]
Derivative Liabilities	(47)	(108)
Fair Value, Measurements, Recurring [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	81	109
Liabilities [Abstract]
Derivative Liabilities	(107)	(129)
Fair Value, Measurements, Recurring [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(1)	3
Liabilities [Abstract]
Derivative Liabilities	1	0
Fair Value, Measurements, Recurring [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	(3)	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents	11	10
Nuclear decommissioning trusts	764	779
Other investments	89	92
Derivative assets [Abstract]
Derivative Assets	287	306
Assets, Fair Value Disclosure	1,151	1,187
Liabilities [Abstract]
Derivative Liabilities	(289)	(309)
Fair Value, Net Asset (Liability)	862	878
Derivative Liabilities, Current	(259)	(268)
Derivative Liabilities, Noncurrent	(30)	(41)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	251	273
Liabilities [Abstract]
Derivative Liabilities	(255)	(277)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	0	0
Liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	36	33
Liabilities [Abstract]
Derivative Liabilities	(34)	(32)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash and Cash Equivalents	47	115
Nuclear decommissioning trusts	431	412
Other investments	49	44
Derivative assets [Abstract]
Derivative Assets	501	351
Assets, Fair Value Disclosure	1,028	922
Liabilities [Abstract]
Derivative Liabilities	(514)	(415)
Fair Value, Net Asset (Liability)	514	507
Derivative Liabilities, Current	(472)	(328)
Derivative Liabilities, Noncurrent	(42)	(87)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	72	89
Liabilities [Abstract]
Derivative Liabilities	(91)	(140)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	426	261
Liabilities [Abstract]
Derivative Liabilities	(413)	(272)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	3	1
Liabilities [Abstract]
Derivative Liabilities	(6)	(2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	(4)	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Cash and Cash Equivalents	0	0
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets [Abstract]
Derivative Assets	138	176
Assets, Fair Value Disclosure	138	176
Liabilities [Abstract]
Derivative Liabilities	(181)	(212)
Fair Value, Net Asset (Liability)	(43)	(36)
Derivative Liabilities, Current	(168)	(177)
Derivative Liabilities, Noncurrent	(13)	(35)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	60	34
Liabilities [Abstract]
Derivative Liabilities	(70)	(86)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	77	139
Liabilities [Abstract]
Derivative Liabilities	(111)	(126)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	1	3
Liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Netting [Member]
Assets [Abstract]
Cash and Cash Equivalents	0	0
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets [Abstract]
Derivative Assets	830	707
Assets, Fair Value Disclosure	830	707
Liabilities [Abstract]
Derivative Liabilities	(828)	(698)
Fair Value, Net Asset (Liability)	2	9
Derivative Liabilities, Current	(759)	(578)
Derivative Liabilities, Noncurrent	(69)	(120)
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	367	382
Liabilities [Abstract]
Derivative Liabilities	(369)	(395)
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	422	291
Liabilities [Abstract]
Derivative Liabilities	(417)	(269)
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	41	34
Liabilities [Abstract]
Derivative Liabilities	(41)	(34)
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	(1)	0
Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	137	224
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	270	277
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	514	400
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	115	139
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	762	592
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	1,350	1,354
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	881	910
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	514	522
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	23	37
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	$ 68	$ 115