Fair Value (Assets and Liabilities Recorded at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets [Abstract]
Nuclear decommissioning trusts	$ 1,237	$ 1,191
Liabilities [Abstract]
Derivative Liabilities, Current	(148)	(195)
Derivative Liabilities, Noncurrent	(29)	(43)
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Cash and Cash Equivalents	108	125
Nuclear decommissioning trusts	1,237	1,191
Other Investments	144	136
Derivative assets [Abstract]
Derivative Assets	124	126
Assets, Fair Value Disclosure	1,613	1,578
Liabilities [Abstract]
Derivative Liabilities	(177)	(238)
Fair Value, Net Asset (Liability)	1,436	1,340
Derivative Liabilities, Current	(148)	(195)
Derivative Liabilities, Noncurrent	(29)	(43)
Fair Value, Measurements, Recurring [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	12	14
Liabilities [Abstract]
Derivative Liabilities	(54)	(108)
Fair Value, Measurements, Recurring [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	106	109
Liabilities [Abstract]
Derivative Liabilities	(122)	(129)
Fair Value, Measurements, Recurring [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	6	3
Liabilities [Abstract]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	(1)	(1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents	12	10
Nuclear decommissioning trusts	798	779
Other Investments	94	92
Derivative assets [Abstract]
Derivative Assets	153	306
Assets, Fair Value Disclosure	1,057	1,187
Liabilities [Abstract]
Derivative Liabilities	(155)	(309)
Fair Value, Net Asset (Liability)	902	878
Derivative Liabilities, Current	(133)	(268)
Derivative Liabilities, Noncurrent	(22)	(41)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	118	273
Liabilities [Abstract]
Derivative Liabilities	(123)	(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	35	33
Liabilities [Abstract]
Derivative Liabilities	(32)	(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	96	115
Nuclear decommissioning trusts	439	412
Other Investments	50	44
Derivative assets [Abstract]
Derivative Assets	602	351
Assets, Fair Value Disclosure	1,187	922
Liabilities [Abstract]
Derivative Liabilities	(615)	(415)
Fair Value, Net Asset (Liability)	572	507
Derivative Liabilities, Current	(528)	(328)
Derivative Liabilities, Noncurrent	(87)	(87)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	101	89
Liabilities [Abstract]
Derivative Liabilities	(123)	(140)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	498	261
Liabilities [Abstract]
Derivative Liabilities	(484)	(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	(7)	(2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	(1)	(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	154	176
Assets, Fair Value Disclosure	154	176
Liabilities [Abstract]
Derivative Liabilities	(194)	(212)
Fair Value, Net Asset (Liability)	(40)	(36)
Derivative Liabilities, Current	(169)	(177)
Derivative Liabilities, Noncurrent	(25)	(35)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	52	34
Liabilities [Abstract]
Derivative Liabilities	(72)	(86)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	95	139
Liabilities [Abstract]
Derivative Liabilities	(122)	(126)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	7	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	(785)	(707)
Assets, Fair Value Disclosure	(785)	(707)
Liabilities [Abstract]
Derivative Liabilities	787	698
Fair Value, Net Asset (Liability)	(2)	9
Derivative Liabilities, Current	682	578
Derivative Liabilities, Noncurrent	105	120
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(259)	(382)
Liabilities [Abstract]
Derivative Liabilities	264	395
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(487)	(291)
Liabilities [Abstract]
Derivative Liabilities	484	269
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Assets	(39)	(34)
Liabilities [Abstract]
Derivative Liabilities	39	34
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other Derivative Contract [Member]
Liabilities [Abstract]
Derivative Liabilities	0	0
Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	206	224
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	145	277
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	618	400
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	123	139
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	(680)	(592)
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	1,407	1,354
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	912	910
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	569	522
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	31	37
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	$ (105)	$ (115)