Segment Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Financial Information
Revenues	[1]	$ 2,976	$ 2,855
Depreciation		294	250
Amortization (deferral) of regulatory assets, net		(148)	83
Miscellaneous income		67	14
Interest expense		250	245
Income taxes (benefits)		252	152
Income (loss) from continuing operations		177	257
Total assets		38,795	43,212	$ 42,257
Goodwill		5,618	5,618	$ 5,618
Property additions		583	588
Regulated Distribution
Segment Financial Information
Revenues		2,321
Regulated Transmission
Segment Financial Information
Income (loss) from continuing operations		99	88
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,576	2,500
Depreciation		196	178
Amortization (deferral) of regulatory assets, net		(152)	81
Miscellaneous income		56	15
Interest expense		128	138
Income taxes (benefits)		93	138
Income (loss) from continuing operations		322	237
Total assets		27,504	27,826
Goodwill		5,004	5,004
Property additions		264	264
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		323	313
Depreciation		61	51
Amortization (deferral) of regulatory assets, net		4	2
Miscellaneous income		4	0
Interest expense		39	39
Income taxes (benefits)		32	52
Total assets		9,681	8,938
Goodwill		614	614
Property additions		292	224
Corporate/Other
Segment Financial Information
Revenues		125	92
Depreciation		19	4
Amortization (deferral) of regulatory assets, net		0	0
Miscellaneous income		16	6
Interest expense		92	75
Income taxes (benefits)		127	(38)
Income (loss) from continuing operations		(244)	(68)
Total assets		1,255	1,160
Goodwill		0	0
Property additions		12	10
Reconciling Adjustments
Segment Financial Information
Revenues		(48)	(50)
Depreciation		18	17
Amortization (deferral) of regulatory assets, net		0	0
Miscellaneous income		(9)	(7)
Interest expense		(9)	(7)
Income taxes (benefits)		0	0
Income (loss) from continuing operations		0	0
Total assets		355	5,288
Goodwill		0	0
Property additions		$ 15	$ 90

[1] Includes excise tax collections of $102 million and $100 million in the three months ended March 31, 2018 and 2017, respectively.