Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Financial Information
Total revenues	$ 2,673	$ 2,963	$ 2,516	$ 2,883	$ 2,710	$ 3,064	$ 2,625	$ 2,862	$ 11,035	[1]	$ 11,261	[1]	$ 10,928	[1]
Provision for depreciation	310	304	309	297	293	283	283	277	1,220		1,136		1,027
Amortization (deferral) of regulatory assets, net									(79)		(150)		308
Miscellaneous income, net									243		205		53
Interest expense									1,033		1,116		1,005
Income taxes	(68)	107	81	93	35	121	101	233	213		490		1,715
Income (loss) from continuing operations	(181)	$ 389	$ 341	$ 355	134	$ 399	$ 308	$ 181	904		1,022		(289)
Total assets	42,301				40,063				42,301		40,063		42,257
Total goodwill	5,618				5,618				5,618		5,618		5,618
Property additions									2,665		2,675		2,587
External revenues
Segment Financial Information
Total revenues									11,035		11,261		10,928
Internal revenues
Segment Financial Information
Total revenues									0		0		0
Regulated Distribution
Segment Financial Information
Total goodwill	5,004								5,004
Regulated Transmission
Segment Financial Information
Total revenues									1,510		1,335
Operating Segments | Regulated Distribution
Segment Financial Information
Total revenues									9,698		10,103		9,760
Provision for depreciation									863		812		724
Amortization (deferral) of regulatory assets, net									(89)		(163)		292
Miscellaneous income, net									174		192		57
Interest expense									495		514		535
Income taxes									271		422		580
Income (loss) from continuing operations									1,076		1,242		916
Total assets	29,642				28,690				29,642		28,690		27,730
Total goodwill	5,004				5,004				5,004		5,004		5,004
Property additions									1,473		1,411		1,191
Operating Segments | Regulated Distribution | External revenues
Segment Financial Information
Total revenues									9,511		9,900		9,602
Operating Segments | Regulated Distribution | Internal revenues
Segment Financial Information
Total revenues									187		203		158
Operating Segments | Regulated Transmission
Segment Financial Information
Total revenues									1,526		1,353		1,324
Provision for depreciation									284		252		224
Amortization (deferral) of regulatory assets, net									10		13		16
Miscellaneous income, net									15		14		1
Interest expense									192		167		156
Income taxes									113		122		205
Income (loss) from continuing operations									447		397		336
Total assets	11,611				10,404				11,611		10,404		9,525
Total goodwill	614				614				614		614		614
Property additions									1,090		1,104		1,030
Operating Segments | Regulated Transmission | External revenues
Segment Financial Information
Total revenues									1,510		1,335		1,307
Operating Segments | Regulated Transmission | Internal revenues
Segment Financial Information
Total revenues									16		18		17
Corporate/ Other
Segment Financial Information
Total revenues									14		34		43
Provision for depreciation									5		3		10
Amortization (deferral) of regulatory assets, net									0		0		0
Miscellaneous income, net									80		32		39
Interest expense									372		468		358
Income taxes									(171)		(54)		930
Income (loss) from continuing operations									(619)		(617)		(1,541)
Total assets	1,015				944				1,015		944		1,007
Total goodwill	0				0				0		0		0
Property additions									102		133		49
Corporate/ Other | External revenues
Segment Financial Information
Total revenues									14		26		19
Corporate/ Other | Internal revenues
Segment Financial Information
Total revenues									0		8		24
Reconciling Adjustments
Segment Financial Information
Total revenues									(203)		(229)		(199)
Provision for depreciation									68		69		69
Amortization (deferral) of regulatory assets, net									0		0		0
Miscellaneous income, net									(26)		(33)		(44)
Interest expense									(26)		(33)		(44)
Income taxes									0		0		0
Income (loss) from continuing operations									0		0		0
Total assets	33				25				33		25		3,995
Total goodwill	$ 0				$ 0				0		0		0
Property additions									0		27		317
Reconciling Adjustments | External revenues
Segment Financial Information
Total revenues									0		0		0
Reconciling Adjustments | Internal revenues
Segment Financial Information
Total revenues									$ (203)		$ (229)		$ (199)

[1] Includes excise and gross receipts tax collections of $373 million, $386 million and $370 million in 2019, 2018 and 2017, respectively.