Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Segment Financial Information
Revenues									$ 14,562		$ 15,026		$ 15,049
Total revenues	$ 3,375	$ 3,917	$ 3,401	$ 3,869	$ 3,541	$ 4,123	$ 3,465	$ 3,897	14,562	[1]	15,026	[1]	15,049	[1]
Depreciation	339	311	334	329	313	328	322	319	1,313		1,282		1,220
Amortization of regulatory assets, net									320		268		12
Impairment of assets	9,218	0	1,447	0	18	8	16	0	10,665		42		0
Investment income (loss)									84		(22)		72
Impairment of equity method investment									0		362		0
Interest expense									1,157		1,132		1,081
Income taxes (benefits)	(3,389)	251	(130)	213	(170)	226	115	144	(3,055)		315		(42)
Income (loss) from continuing operations									(6,177)		578		213
Discontinued operations, net of tax									0		0		86
NET INCOME (LOSS)	(5,796)	$ 380	$ (1,089)	$ 328	(226)	$ 395	$ 187	$ 222	(6,177)		578		299
Total assets	43,148				52,094				43,148		52,094		51,552
Total goodwill	5,618				6,418				5,618		6,418		6,418
Property additions									2,835		2,704		3,312
Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Regulated Distribution
Segment Financial Information
Revenues									9,629		9,582		9,054
Total revenues									9,629		9,582		9,054
Depreciation									676		664		651
Amortization of regulatory assets, net									313		261		1
Impairment of assets									0		8
Investment income (loss)									49		42		56
Impairment of equity method investment											0
Interest expense									586		600		603
Income taxes (benefits)									375		325		209
Income (loss) from continuing operations													433
Discontinued operations, net of tax													0
NET INCOME (LOSS)									651		588		433
Total assets	27,702				27,390				27,702		27,390		27,332
Total goodwill	5,004				5,092				5,004		5,092		5,092
Property additions									1,063		1,040		855
Regulated Distribution | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Regulated Transmission
Segment Financial Information
Revenues									1,151		1,054		817
Total revenues									1,151		1,054		817
Depreciation									187		164		134
Amortization of regulatory assets, net									7		7		11
Impairment of assets									0		0
Investment income (loss)									0		0		0
Impairment of equity method investment											0
Interest expense									158		147		117
Income taxes (benefits)									187		191		139
Income (loss) from continuing operations													255
Discontinued operations, net of tax													0
NET INCOME (LOSS)									331		328		255
Total assets	8,755				7,800				8,755		7,800		6,864
Total goodwill	614				526				614		526		526
Property additions									1,101		1,020		1,446
Regulated Transmission | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Competitive Energy Services
Segment Financial Information
Revenues									4,070		4,698		5,470
Total revenues									4,549		5,384		6,289
Depreciation									387		394		387
Amortization of regulatory assets, net									0		0		0
Impairment of assets									10,665		34
Investment income (loss)									66		(16)		54
Impairment of equity method investment											0
Interest expense									194		192		197
Income taxes (benefits)									(3,498)		50		(223)
Income (loss) from continuing operations													(417)
Discontinued operations, net of tax													86
NET INCOME (LOSS)									(6,919)		89		(331)
Total assets	5,952				16,027				5,952		16,027		16,180
Total goodwill	0				800				0		800		800
Property additions									619		588		939
Competitive Energy Services | Intersegment Eliminations
Segment Financial Information
Revenues									479		686		819
Other/Corporate
Segment Financial Information
Revenues									0		0		0
Total revenues									0		0		0
Depreciation									63		60		48
Amortization of regulatory assets, net									0		0		0
Impairment of assets									0		0
Investment income (loss)									10		(9)		2
Impairment of equity method investment											362
Interest expense									219		193		168
Income taxes (benefits)									(121)		(262)		(178)
Income (loss) from continuing operations													(58)
Discontinued operations, net of tax													0
NET INCOME (LOSS)									(240)		(427)		(58)
Total assets	739				877				739		877		1,176
Total goodwill	0				0				0		0		0
Property additions									52		56		72
Other/Corporate | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Reconciling Adjustments
Segment Financial Information
Revenues									(288)		(308)		(292)
Total revenues									(767)		(994)		(1,111)
Depreciation									0		0		0
Amortization of regulatory assets, net									0		0		0
Impairment of assets									0		0
Investment income (loss)									(41)		(39)		(40)
Impairment of equity method investment											0
Interest expense									0		0		(4)
Income taxes (benefits)									2		11		11
Income (loss) from continuing operations													0
Discontinued operations, net of tax													0
NET INCOME (LOSS)									0		0		0
Total assets	0				0				0		0		0
Total goodwill	$ 0				$ 0				0		0		0
Property additions									0		0		0
Reconciling Adjustments | Intersegment Eliminations
Segment Financial Information
Revenues									$ (479)		$ (686)		$ (819)

[1] Includes excise tax collections of $406 million, $416 million and $420 million in 2016, 2015 and 2014, respectively.