Fair Value (Assets and Liabilities Recorded at Fair Value on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Assets [Abstract]
Nuclear decommissioning trusts	$ 1,229	$ 1,191
Derivative assets [Abstract]
Derivative Asset, Gross	693	833
Derivative Assets, Net	97	126
Liabilities [Abstract]
Derivative Liability, Gross	787	936
Derivative Liabilities, Net	(153)	(238)
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Cash and Cash Equivalents	62	125
Nuclear decommissioning trusts	1,229	1,191
Other Investments	146	136
Derivative assets [Abstract]
Derivative Assets, Net	97	126
Assets, Fair Value Disclosure	1,534	1,578
Liabilities [Abstract]
Derivative Liabilities, Net	(153)	(238)
Fair Value, Net Asset (Liability)	1,381	1,340
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Cash and Cash Equivalents	11	10
Nuclear decommissioning trusts	789	779
Other Investments	95	92
Derivative assets [Abstract]
Derivative Asset, Gross	164	306
Assets, Fair Value Disclosure	1,059	1,187
Liabilities [Abstract]
Derivative Liability, Gross	168	309
Fair Value, Net Asset (Liability)	891	878
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Cash and Cash Equivalents	51	115
Nuclear decommissioning trusts	440	412
Other Investments	51	44
Derivative assets [Abstract]
Derivative Asset, Gross	413	351
Assets, Fair Value Disclosure	955	922
Liabilities [Abstract]
Derivative Liability, Gross	461	415
Fair Value, Net Asset (Liability)	494	507
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 Asset, Gross	116	176
Assets, Fair Value Disclosure	116	176
Liabilities [Abstract]
Derivative Liability, Gross	158	212
Fair Value, Net Asset (Liability)	(42)	(36)
Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	130	224
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	155	277
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	419	400
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	93	139
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	1,404	1,354
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	904	910
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	536	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
Current Derivative Liability [Member]
Liabilities [Abstract]
Derivative Liability, Gross	696	773
Current Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities [Abstract]
Derivative Liabilities, Net	(134)	(195)
Current Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	146	268
Current Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	405	328
Current Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	145	177
Noncurrent Derivative Liability [Member]
Liabilities [Abstract]
Derivative Liability, Gross	91	163
Noncurrent Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities [Abstract]
Derivative Liabilities, Net	(19)	(43)
Noncurrent Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	22	41
Noncurrent Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	56	87
Noncurrent Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities [Abstract]
Derivative Liability, Gross	13	35
Fair Value, Master Netting Arrangements [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(596)	(707)
Liabilities [Abstract]
Derivative Liability, Gross	(634)	(698)
Fair Value, Master Netting Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(596)	(707)
Assets, Fair Value Disclosure	(596)	(707)
Liabilities [Abstract]
Derivative Liability, Gross	(634)	(698)
Fair Value, Net Asset (Liability)	(38)	9
Fair Value, Master Netting Arrangements [Member] | Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	(537)	(592)
Fair Value, Master Netting Arrangements [Member] | Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Assets, Fair Value Disclosure	(59)	(115)
Fair Value, Master Netting Arrangements [Member] | Current Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities [Abstract]
Derivative Liability, Gross	(562)	(578)
Fair Value, Master Netting Arrangements [Member] | Noncurrent Derivative Liability [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities [Abstract]
Derivative Liability, Gross	(72)	(120)
Natural Gas Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	254	396
Derivative Assets, Net	29	14
Liabilities [Abstract]
Derivative Liability, Gross	342	503
Derivative Liabilities, Net	(74)	(108)
Natural Gas Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Assets, Net	29	14
Liabilities [Abstract]
Derivative Liabilities, Net	(74)	(108)
Natural Gas Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	118	273
Liabilities [Abstract]
Derivative Liability, Gross	129	277
Natural Gas Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	98	89
Liabilities [Abstract]
Derivative Liability, Gross	147	140
Natural Gas Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	38	34
Liabilities [Abstract]
Derivative Liability, Gross	66	86
Natural Gas Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(225)	(382)
Liabilities [Abstract]
Derivative Liability, Gross	(268)	(395)
Natural Gas Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(225)	(382)
Liabilities [Abstract]
Derivative Liability, Gross	(268)	(395)
Electricity Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	386	400
Derivative Assets, Net	64	109
Liabilities [Abstract]
Derivative Liability, Gross	394	398
Derivative Liabilities, Net	(77)	(129)
Electricity Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Assets, Net	64	109
Liabilities [Abstract]
Derivative Liabilities, Net	(77)	(129)
Electricity Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	0	0
Liabilities [Abstract]
Derivative Liability, Gross	0	0
Electricity Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	312	261
Liabilities [Abstract]
Derivative Liability, Gross	303	272
Electricity Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	74	139
Liabilities [Abstract]
Derivative Liability, Gross	91	126
Electricity Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(322)	(291)
Liabilities [Abstract]
Derivative Liability, Gross	(317)	(269)
Electricity Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(322)	(291)
Liabilities [Abstract]
Derivative Liability, Gross	(317)	(269)
Other Commodity Contract [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	52	37
Derivative Assets, Net	4	3
Liabilities [Abstract]
Derivative Liability, Gross	48	34
Derivative Liabilities, Net	0	0
Other Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Assets, Net	4	3
Liabilities [Abstract]
Derivative Liabilities, Net	0	0
Other Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	46	33
Liabilities [Abstract]
Derivative Liability, Gross	39	32
Other Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	2	1
Liabilities [Abstract]
Derivative Liability, Gross	8	2
Other Commodity Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	4	3
Liabilities [Abstract]
Derivative Liability, Gross	1	0
Other Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(48)	(34)
Liabilities [Abstract]
Derivative Liability, Gross	(48)	(34)
Other Commodity Contract [Member] | Fair Value, Master Netting Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(48)	(34)
Liabilities [Abstract]
Derivative Liability, Gross	(48)	(34)
Other Derivative Contract [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	1	0
Derivative Assets, Net	0	0
Liabilities [Abstract]
Derivative Liability, Gross	3	1
Derivative Liabilities, Net	(2)	(1)
Other Derivative Contract [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Assets, Net	0	0
Liabilities [Abstract]
Derivative Liabilities, Net	(2)	(1)
Other Derivative Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	0	0
Liabilities [Abstract]
Derivative Liability, Gross	0	0
Other Derivative Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	1	0
Liabilities [Abstract]
Derivative Liability, Gross	3	1
Other Derivative Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	0	0
Liabilities [Abstract]
Derivative Liability, Gross	0	0
Other Derivative Contract [Member] | Fair Value, Master Netting Arrangements [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(1)	0
Liabilities [Abstract]
Derivative Liability, Gross	(1)	0
Other Derivative Contract [Member] | Fair Value, Master Netting Arrangements [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets [Abstract]
Derivative Asset, Gross	(1)	0
Liabilities [Abstract]
Derivative Liability, Gross	$ (1)	$ 0