Fair Value (Assets and Liabilities Recorded at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative liabilities [Abstract]
Derivative Liabilities, Current	$ (195)	$ (125)
Derivative Liabilities, Noncurrent	(43)	(26)
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	125	123
Nuclear decommissioning trusts	1,191	1,037
Other investments	136	110
Derivative assets [Abstract]
Derivative Assets	126	147
Assets, Fair Value Disclosure	1,578	1,417
Derivative liabilities [Abstract]
Derivative Liabilities	(238)	(151)
Derivative Liabilities, Current	(195)	(125)
Derivative Liabilities, Noncurrent	(43)	(26)
Fair Value, Net Asset (Liability)	1,340	1,266
Fair Value, Measurements, Recurring [Member] | Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	224	231
Fair Value, Measurements, Recurring [Member] | Non Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	1,354	1,186
Fair Value, Measurements, Recurring [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	14	40
Derivative liabilities [Abstract]
Derivative Liabilities	(108)	(56)
Fair Value, Measurements, Recurring [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	109	102
Derivative liabilities [Abstract]
Derivative Liabilities	(129)	(93)
Fair Value, Measurements, Recurring [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	3	5
Derivative liabilities [Abstract]
Derivative Liabilities	0	(1)
Fair Value, Measurements, Recurring [Member] | Other Contract [Member]
Derivative liabilities [Abstract]
Derivative Liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	10	0
Nuclear decommissioning trusts	779	694
Other investments	92	66
Derivative assets [Abstract]
Derivative Assets	306	561
Assets, Fair Value Disclosure	1,187	1,321
Derivative liabilities [Abstract]
Derivative Liabilities	(309)	(532)
Derivative Liabilities, Current	(268)	(466)
Derivative Liabilities, Noncurrent	(41)	(66)
Fair Value, Net Asset (Liability)	878	789
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	277	493
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Non Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	910	828
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	273	555
Derivative liabilities [Abstract]
Derivative Liabilities	(277)	(526)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	0	0
Derivative 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	33	6
Derivative liabilities [Abstract]
Derivative Liabilities	(32)	(6)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Contract [Member]
Derivative liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	115	123
Nuclear decommissioning trusts	412	343
Other investments	44	44
Derivative assets [Abstract]
Derivative Assets	351	295
Assets, Fair Value Disclosure	922	805
Derivative liabilities [Abstract]
Derivative Liabilities	(415)	(315)
Derivative Liabilities, Current	(328)	(269)
Derivative Liabilities, Noncurrent	(87)	(46)
Fair Value, Net Asset (Liability)	507	490
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	400	372
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Non Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	522	433
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	89	66
Derivative liabilities [Abstract]
Derivative Liabilities	(140)	(73)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	261	226
Derivative liabilities [Abstract]
Derivative Liabilities	(272)	(240)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	1	3
Derivative liabilities [Abstract]
Derivative Liabilities	(2)	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Contract [Member]
Derivative liabilities [Abstract]
Derivative Liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member] | 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 assets [Abstract]
Derivative Assets	176	160
Assets, Fair Value Disclosure	176	160
Derivative liabilities [Abstract]
Derivative Liabilities	(212)	(173)
Derivative Liabilities, Current	(177)	(144)
Derivative Liabilities, Noncurrent	(35)	(29)
Fair Value, Net Asset (Liability)	(36)	(13)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	139	120
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Non Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	37	40
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	34	24
Derivative liabilities [Abstract]
Derivative Liabilities	(86)	(62)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	139	134
Derivative liabilities [Abstract]
Derivative Liabilities	(126)	(111)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	3	2
Derivative liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Contract [Member]
Derivative liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member]
Assets [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Nuclear decommissioning trusts	0	0
Other investments	0	0
Derivative assets [Abstract]
Derivative Assets	(707)	(869)
Assets, Fair Value Disclosure	(707)	(869)
Derivative liabilities [Abstract]
Derivative Liabilities	698	869
Derivative Liabilities, Current	578	754
Derivative Liabilities, Noncurrent	120	115
Fair Value, Net Asset (Liability)	9	0
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	(592)	(754)
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Non Current Asset [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	(115)	(115)
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(382)	(605)
Derivative liabilities [Abstract]
Derivative Liabilities	395	605
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(291)	(258)
Derivative liabilities [Abstract]
Derivative Liabilities	269	258
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(34)	(6)
Derivative liabilities [Abstract]
Derivative Liabilities	34	6
Fair Value, Measurements, Recurring [Member] | Netting Adjustments [Member] | Other Contract [Member]
Derivative liabilities [Abstract]
Derivative Liabilities	$ 0	$ 0