Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Segment Reporting Information [Line Items]
NET INCOME (LOSS)	$ (2,499)	$ 396	$ 174	$ 205	$ (5,796)	$ 380	$ (1,089)	$ 328	$ (1,724)		$ (6,177)		$ 578
Segment Financial Information
Revenues									14,017		14,562		15,026
Total revenues	3,442	3,714	3,309	3,552	3,375	3,917	3,401	3,869	14,017	[1]	14,562	[1]	15,026	[1]
Depreciation	293	289	281	275	339	311	334	329	1,138		1,313		1,282
Amortization of regulatory assets, net									308		297		172
Impairment of assets and related charges	2,244	31	131	0	9,218	0	1,447	0	2,406		10,665		42
Investment income (loss)									98		84		(22)
Impairment of equity method investment									0		0		362
Interest expense									1,178		1,157		1,132
Income taxes (benefits)	413	$ 239	$ 117	$ 126	(3,389)	$ 251	(130)	$ 213	895		(3,055)		315
Total assets	42,257				43,148				42,257		43,148		52,094
Total goodwill	5,618				5,618				5,618		5,618		6,418
Property additions									2,587		2,835		2,704
Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Regulated Distribution
Segment Reporting Information [Line Items]
NET INCOME (LOSS)									916		651		588
Segment Financial Information
Revenues									9,734		9,629		9,582
Total revenues									9,734		9,629		9,582
Depreciation									724		676		664
Amortization of regulatory assets, net									292		290		165
Impairment of assets and related charges									0		0		8
Investment income (loss)									54		49		42
Impairment of equity method investment													0
Interest expense									535		586		600
Income taxes (benefits)									580		375		325
Total assets	27,730				27,702				27,730		27,702		27,390
Total goodwill	5,004				5,004				5,004		5,004		5,092
Property additions									1,191		1,063		1,040
Regulated Distribution | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Regulated Transmission
Segment Reporting Information [Line Items]
NET INCOME (LOSS)									336		331		328
Segment Financial Information
Revenues									1,325		1,144		1,046
Total revenues									1,325		1,144		1,046
Depreciation									224		187		164
Amortization of regulatory assets, net									16		7		7
Impairment of assets and related charges									41		0		0
Investment income (loss)									0		0		0
Impairment of equity method investment													0
Interest expense									156		158		147
Income taxes (benefits)									205		187		191
Total assets	9,525				8,755				9,525		8,755		7,800
Total goodwill	614				614				614		614		526
Property additions									1,030		1,101		1,020
Regulated Transmission | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Competitive Energy Services
Segment Reporting Information [Line Items]
NET INCOME (LOSS)									(2,641)		(6,919)		89
Segment Financial Information
Revenues									3,143		4,070		4,698
Total revenues									3,529		4,549		5,384
Depreciation									118		387		394
Amortization of regulatory assets, net									0		0		0
Impairment of assets and related charges							$ 647		2,365		10,665		34
Investment income (loss)									81		66		(16)
Impairment of equity method investment													0
Interest expense									179		194		192
Income taxes (benefits)									155		(3,498)		50
Total assets	4,339				5,952				4,339		5,952		16,027
Total goodwill	0				0				0		0		800
Property additions									317		619		588
Competitive Energy Services | Intersegment Eliminations
Segment Financial Information
Revenues									386		479		686
Other/Corporate
Segment Reporting Information [Line Items]
NET INCOME (LOSS)									(335)		(240)		(427)
Segment Financial Information
Revenues									0		0		0
Total revenues									0		0		0
Depreciation									72		63		60
Amortization of regulatory assets, net									0		0		0
Impairment of assets and related charges									0		0		0
Investment income (loss)									11		10		(9)
Impairment of equity method investment													362
Interest expense									308		219		193
Income taxes (benefits)									(45)		(119)		(251)
Total assets	663				739				663		739		877
Total goodwill	0				0				0		0		0
Property additions									49		52		56
Other/Corporate | Intersegment Eliminations
Segment Financial Information
Revenues									0		0		0
Reconciling Adjustments
Segment Reporting Information [Line Items]
NET INCOME (LOSS)									0		0		0
Segment Financial Information
Revenues									(185)		(281)		(300)
Total revenues									(571)		(760)		(986)
Depreciation									0		0		0
Amortization of regulatory assets, net									0		0		0
Impairment of assets and related charges									0		0		0
Investment income (loss)									(48)		(41)		(39)
Impairment of equity method investment													0
Interest expense									0		0		0
Income taxes (benefits)									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									$ (386)		$ (479)		$ (686)

[1] Includes excise tax collections of $390 million, $406 million and $416 million in 2017, 2016 and 2015, respectively.