Segment Information - Financial Data (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Financial Information
Revenues	[1]	$ 2,516	$ 2,625	$ 5,399	$ 5,487
Depreciation		309	283	606	560
Amortization (deferral) of regulatory assets, net		37	(107)	42	(255)
Miscellaneous income (expense), net		80	48	134	115
Interest expense		259	355	512	603
Income taxes (benefits)		81	101	174	334
Income (loss) from continuing operations		341	308	696	489
Total assets		40,884		40,884		$ 40,063
Goodwill		5,618		5,618		5,618
Property additions		674	724	1,228	1,307
External Customers
Segment Financial Information
Revenues		2,516	2,625	5,399	5,487
Internal Customers
Segment Financial Information
Revenues		0	0	0	0
Regulated Distribution
Segment Financial Information
Revenues		1,966	2,110	4,310	4,431
Income (loss) from continuing operations				587	699
Regulated Transmission
Segment Financial Information
Revenues		367	336	719	655
Income (loss) from continuing operations		116	104	220	203
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,192	2,352	4,765	4,928
Depreciation		220	200	429	396
Amortization (deferral) of regulatory assets, net		34	(107)	37	(259)
Miscellaneous income (expense), net		46	56	92	112
Interest expense		124	129	246	257
Income taxes (benefits)		67	138	156	231
Income (loss) from continuing operations		258	377
Total assets		29,240		29,240		28,690
Goodwill		5,004		5,004		5,004
Property additions		354	391	672	655
Operating Segments | Regulated Distribution | External Customers
Segment Financial Information
Revenues		2,145	2,285	4,671	4,823
Operating Segments | Regulated Distribution | Internal Customers
Segment Financial Information
Revenues		47	67	94	105
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		372	341	728	664
Depreciation		71	62	140	123
Amortization (deferral) of regulatory assets, net		3	0	5	4
Miscellaneous income (expense), net		4	3	8	7
Interest expense		48	42	93	81
Income taxes (benefits)		30	38	61	70
Total assets		11,070		11,070		10,404
Goodwill		614		614		614
Property additions		300	282	531	574
Operating Segments | Regulated Transmission | External Customers
Segment Financial Information
Revenues		368	336	720	655
Operating Segments | Regulated Transmission | Internal Customers
Segment Financial Information
Revenues		4	5	8	9
Corporate/Other
Segment Financial Information
Revenues		3	11	8	22
Depreciation		1	3	3	5
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		38	(1)	49	15
Interest expense		95	194	188	284
Income taxes (benefits)		(16)	(75)	(43)	33
Income (loss) from continuing operations		(33)	(173)	(111)	(413)
Total assets		574		574		969
Goodwill		0		0		0
Property additions		20	44	25	55
Corporate/Other | External Customers
Segment Financial Information
Revenues		3	4	8	9
Corporate/Other | Internal Customers
Segment Financial Information
Revenues		0	7	0	13
Reconciling Adjustments
Segment Financial Information
Revenues		(51)	(79)	(102)	(127)
Depreciation		17	18	34	36
Amortization (deferral) of regulatory assets, net		0	0	0	0
Miscellaneous income (expense), net		(8)	(10)	(15)	(19)
Interest expense		(8)	(10)	(15)	(19)
Income taxes (benefits)		0	0	0	0
Income (loss) from continuing operations		0	0	0	0
Total assets		0		0		0
Goodwill		0		0		$ 0
Property additions		0	7	0	23
Reconciling Adjustments | External Customers
Segment Financial Information
Revenues		0	0	0	0
Reconciling Adjustments | Internal Customers
Segment Financial Information
Revenues		$ (51)	$ (79)	$ (102)	$ (127)

[1] Includes excise and gross receipts tax collections of $81 million and $87 million during the three months ended June 30, 2019 and 2018, respectively, and $183 million and $189 million during the six months ended June 30, 2019 and 2018, respectively.