Segment Information - Financial Data (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Financial Information
Revenues	[1]	$ 2,963	$ 3,064	$ 8,362	$ 8,551
Depreciation		304	283	910	843
Amortization (deferral) of regulatory assets, net		43	67	85	(188)
Miscellaneous income (expense), net		57	49	191	164
Interest expense		261	255	773	858
Income taxes (benefits)		107	121	281	455
Income (loss) from continuing operations		389	399	1,085	888
Total assets		41,506		41,506		$ 40,063
Goodwill		5,618		5,618		5,618
Property additions		684	635	1,912	1,942
External Customers
Segment Financial Information
Revenues		2,963	3,064	8,362	8,551
Internal Customers
Segment Financial Information
Revenues		0	0	0	0
Regulated Distribution
Segment Financial Information
Revenues		2,446	2,499	6,756	6,930
Income (loss) from continuing operations				957	1,115
Regulated Transmission
Segment Financial Information
Revenues		371	341	1,090	996
Income (loss) from continuing operations		113	99	333	302
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,636	2,766	7,401	7,694
Depreciation		215	202	644	598
Amortization (deferral) of regulatory assets, net		42	65	79	(194)
Miscellaneous income (expense), net		36	34	128	146
Interest expense		124	127	370	384
Income taxes (benefits)		103	126	259	357
Income (loss) from continuing operations		370	416
Total assets		29,428		29,428		28,690
Goodwill		5,004		5,004		5,004
Property additions		365	356	1,037	1,011
Operating Segments | Regulated Distribution | External Customers
Segment Financial Information
Revenues		2,590	2,717	7,261	7,540
Operating Segments | Regulated Distribution | Internal Customers
Segment Financial Information
Revenues		46	49	140	154
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		375	346	1,103	1,010
Depreciation		71	64	211	187
Amortization (deferral) of regulatory assets, net		1	2	6	6
Miscellaneous income (expense), net		4	4	12	11
Interest expense		49	43	142	124
Income taxes (benefits)		26	34	87	104
Total assets		11,255		11,255		10,404
Goodwill		614		614		614
Property additions		304	262	835	836
Operating Segments | Regulated Transmission | External Customers
Segment Financial Information
Revenues		371	341	1,091	996
Operating Segments | Regulated Transmission | Internal Customers
Segment Financial Information
Revenues		4	5	12	14
Corporate/Other
Segment Financial Information
Revenues		2	6	10	28
Depreciation		0	1	3	6
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		24	19	73	34
Interest expense		95	93	283	377
Income taxes (benefits)		(22)	(39)	(65)	(6)
Income (loss) from continuing operations		(94)	(116)	(205)	(529)
Total assets		790		790		944
Goodwill		0		0		0
Property additions		15	5	40	68
Corporate/Other | External Customers
Segment Financial Information
Revenues		2	6	10	15
Corporate/Other | Internal Customers
Segment Financial Information
Revenues		0	0	0	13
Reconciling Adjustments
Segment Financial Information
Revenues		(50)	(54)	(152)	(181)
Depreciation		18	16	52	52
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		(7)	(8)	(22)	(27)
Interest expense		(7)	(8)	(22)	(27)
Income taxes (benefits)		0	0	0	0
Income (loss) from continuing operations		0	0	0	0
Total assets		33		33		25
Goodwill		0		0		$ 0
Property additions		0	12	0	27
Reconciling Adjustments | External Customers
Segment Financial Information
Revenues		0	0	0	0
Reconciling Adjustments | Internal Customers
Segment Financial Information
Revenues		$ (50)	$ (54)	$ (152)	$ (181)

[1] Includes excise and gross receipts tax collections of $100 million and $104 million during the three months ended September 30, 2019 and 2018, respectively, and $283 million and $293 million during the nine months ended September 30, 2019 and 2018, respectively.