Segment Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Financial Information
Revenues	[1]	$ 3,064	$ 2,910	$ 8,551	$ 8,247
Depreciation		283	261	843	765
Amortization (deferral) of regulatory assets, net		67	113	(188)	274
Impairment of assets		0	13	0	13
Miscellaneous income (expense), net		49	19	164	44
Interest expense		255	262	858	751
Income taxes (benefits)		133	202	503	483
Income (loss) from continuing operations		387	301	840	772
Total assets		39,443	43,649	39,443	43,649	$ 42,257
Goodwill		5,618	5,618	5,618	5,618	$ 5,618
Property additions		635	593	1,942	1,847
Regulated Distribution
Segment Financial Information
Revenues		2,499		6,930
Income (loss) from continuing operations				1,115	756
Regulated Transmission
Segment Financial Information
Revenues		341		996
Income (loss) from continuing operations		99	84	302	264
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,766	2,609	7,694	7,380
Depreciation		202	183	598	540
Amortization (deferral) of regulatory assets, net		65	107	(194)	263
Impairment of assets			0		0
Miscellaneous income (expense), net		34	16	146	45
Interest expense		127	133	384	405
Income taxes (benefits)		126	183	357	442
Income (loss) from continuing operations		416	314
Total assets		28,530	27,866	28,530	27,866
Goodwill		5,004	5,004	5,004	5,004
Property additions		356	286	1,011	854
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		346	341	1,010	981
Depreciation		64	59	187	164
Amortization (deferral) of regulatory assets, net		2	6	6	11
Impairment of assets			13		13
Miscellaneous income (expense), net		4	1	11	1
Interest expense		43	38	124	116
Income taxes (benefits)		34	49	104	154
Total assets		10,017	9,356	10,017	9,356
Goodwill		614	614	614	614
Property additions		262	248	836	717
Corporate/Other
Segment Financial Information
Revenues		6	10	28	37
Depreciation		1	2	6	9
Amortization (deferral) of regulatory assets, net		0	0	0	0
Impairment of assets			0		0
Miscellaneous income (expense), net		19	15	34	31
Interest expense		93	104	377	263
Income taxes (benefits)		(27)	(30)	42	(113)
Income (loss) from continuing operations		(128)	(97)	(577)	(248)
Total assets		896	938	896	938
Goodwill		0	0	0	0
Property additions		5	14	68	43
Reconciling Adjustments
Segment Financial Information
Revenues		(54)	(50)	(181)	(151)
Depreciation		16	17	52	52
Amortization (deferral) of regulatory assets, net		0	0	0	0
Impairment of assets			0		0
Miscellaneous income (expense), net		(8)	(13)	(27)	(33)
Interest expense		(8)	(13)	(27)	(33)
Income taxes (benefits)		0	0	0	0
Income (loss) from continuing operations		0	0	0	0
Total assets		0	5,489	0	5,489
Goodwill		0	0	0	0
Property additions		$ 12	$ 45	$ 27	$ 233

[1] Includes excise tax collections of $104 million and $102 million in the three months ended September 30, 2018 and 2017, respectively, and $293 million in the nine months ended September 30, 2018 and 2017.