Segment Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Segment Financial Information
Total revenues	$ 2,710	$ 3,064	$ 2,625	$ 2,862	$ 2,681	$ 2,910	$ 2,561	$ 2,776	$ 11,261	[1]	$ 10,928	[1]	$ 10,700	[1]
Provision for depreciation	293	283	283	277	262	261	254	250	1,136		1,027		933
Amortization (deferral) of regulatory assets, net									(150)		308		297
Impairment of assets and related charges	0	0	0	0	28	13	0	0	0		41		43
Miscellaneous income, net									205		53		44
Interest expense									1,116		1,005		973
Income taxes	(13)	133	121	249	1,232	202	132	149	490		1,715		527
Income (loss) from continuing operations	182	$ 387	$ 288	$ 165	(1,061)	$ 301	$ 220	$ 251	1,022		(289)		551
Total assets	40,063				42,257				40,063		42,257		43,148
Total goodwill	5,618				5,618				5,618		5,618		5,618
Property additions									2,675		2,587		2,835
Regulated Distribution
Segment Financial Information
Total goodwill	5,004								5,004
Regulated Transmission
Segment Financial Information
Total revenues									1,335
Operating Segments | Regulated Distribution
Segment Financial Information
Total revenues									10,103		9,760		9,619
Provision for depreciation									812		724		676
Amortization (deferral) of regulatory assets, net									(163)		292		290
Impairment of assets and related charges											0		0
Miscellaneous income, net									192		57		85
Interest expense									514		535		586
Income taxes									422		580		375
Income (loss) from continuing operations									1,242		916		651
Total assets	28,690				27,730				28,690		27,730		27,702
Total goodwill	5,004				5,004				5,004		5,004		5,004
Property additions									1,411		1,191		1,063
Operating Segments | Regulated Transmission
Segment Financial Information
Total revenues									1,353		1,324		1,143
Provision for depreciation									252		224		187
Amortization (deferral) of regulatory assets, net									13		16		7
Impairment of assets and related charges											41		0
Miscellaneous income, net									14		1		(1)
Interest expense									167		156		158
Income taxes									122		205		187
Income (loss) from continuing operations									397		336		331
Total assets	10,404				9,525				10,404		9,525		8,755
Total goodwill	614				614				614		614		614
Property additions									1,104		1,030		1,101
Corporate/ Other
Segment Financial Information
Total revenues									34		43		140
Provision for depreciation									3		10		3
Amortization (deferral) of regulatory assets, net									0		0		0
Impairment of assets and related charges											0		43
Miscellaneous income, net									32		39		(17)
Interest expense									468		358		252
Income taxes									(54)		930		(35)
Income (loss) from continuing operations									(617)		(1,541)		(431)
Total assets	969				1,007				969		1,007		1,061
Total goodwill	0				0				0		0		0
Property additions									133		49		56
Reconciling Adjustments
Segment Financial Information
Total revenues									(229)		(199)		(202)
Provision for depreciation									69		69		67
Amortization (deferral) of regulatory assets, net									0		0		0
Impairment of assets and related charges											0		0
Miscellaneous income, net									(33)		(44)		(23)
Interest expense									(33)		(44)		(23)
Income taxes									0		0		0
Income (loss) from continuing operations									0		0		0
Total assets	0				3,995				0		3,995		5,630
Total goodwill	$ 0				$ 0				0		0		0
Property additions									$ 27		$ 317		$ 615

[1] Includes excise and gross receipts tax collections of $386 million, $370 million and $378 million in 2018, 2017 and 2016, respectively.