Segment Information (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Financial Information
Revenues	[1]	$ 2,704	$ 2,624	$ 5,680	$ 5,479
Depreciation		299	254	593	504
Amortization (deferral) of regulatory assets, net		(107)	78	(255)	161
Miscellaneous income (expense), net		48	11	115	25
Interest expense		369	248	619	493
Income taxes (benefits)		115	132	367	284
Income (loss) from continuing operations		267	219	444	476
Total assets		38,971	43,327	38,971	43,327	$ 42,257
Goodwill		5,618	5,618	5,618	5,618	$ 5,618
Property additions		724	666	1,307	1,254
Regulated Distribution
Segment Financial Information
Revenues		2,110		4,431
Income (loss) from continuing operations				699	442
Regulated Transmission
Segment Financial Information
Income (loss) from continuing operations		104	92	203	180
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,352	2,271	4,928	4,771
Depreciation		200	179	396	357
Amortization (deferral) of regulatory assets, net		(107)	75	(259)	156
Miscellaneous income (expense), net		56	14	112	29
Interest expense		129	134	257	272
Income taxes (benefits)		138	121	231	259
Income (loss) from continuing operations		377	205
Total assets		28,088	27,660	28,088	27,660
Goodwill		5,004	5,004	5,004	5,004
Property additions		391	304	655	568
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		341	327	664	640
Depreciation		62	54	123	105
Amortization (deferral) of regulatory assets, net		0	3	4	5
Miscellaneous income (expense), net		3	0	7	0
Interest expense		42	39	81	78
Income taxes (benefits)		38	53	70	105
Total assets		9,833	9,142	9,833	9,142
Goodwill		614	614	614	614
Property additions		282	245	574	469
Corporate/Other
Segment Financial Information
Revenues		86	77	211	169
Depreciation		19	3	38	7
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		(1)	10	15	16
Interest expense		208	88	300	163
Income taxes (benefits)		(61)	(42)	66	(80)
Income (loss) from continuing operations		(214)	(78)	(458)	(146)
Total assets		1,050	1,190	1,050	1,190
Goodwill		0	0	0	0
Property additions		51	29	63	39
Reconciling Adjustments
Segment Financial Information
Revenues		(75)	(51)	(123)	(101)
Depreciation		18	18	36	35
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		(10)	(13)	(19)	(20)
Interest expense		(10)	(13)	(19)	(20)
Income taxes (benefits)		0	0	0	0
Income (loss) from continuing operations		0	0	0	0
Total assets		0	5,335	0	5,335
Goodwill		0	0	0	0
Property additions		$ 0	$ 88	$ 15	$ 178

[1] Includes excise tax collections of $87 million and $91 million in the three months ended June 30, 2018 and 2017, respectively, and $189 million and $191 million in the six months ended June 30, 2018 and 2017, respectively.