Segment Information - Financial Data (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Financial Information
Revenues	[1]	$ 3,124	$ 3,022	$ 8,472	$ 8,253
Depreciation		326	316	972	954
Amortization (deferral) of regulatory assets, net		30	(91)	171	(26)
DPA penalty (Note 9)		0	0	230	0
Miscellaneous income (expense), net		136	100	379	303
Interest expense		283	266	855	792
Income taxes (benefits)		88	116	271	122
Income (loss) from continuing operations		416	460	809	791
Property additions		542	687	1,768	1,979
Total assets		43,854		43,854		$ 44,464
Goodwill		5,618		5,618		5,618
External Customers
Segment Financial Information
Revenues		3,124	3,022	8,472	8,253
Internal Customers
Segment Financial Information
Revenues		0	0	0	0
Operating Segments | Regulated Distribution
Segment Financial Information
Revenues		2,759	2,661	7,387	7,207
Depreciation		229	223	684	672
Amortization (deferral) of regulatory assets, net		29	(91)	159	(32)
DPA penalty (Note 9)				0
Miscellaneous income (expense), net		102	81	297	246
Interest expense		133	124	392	374
Income taxes (benefits)		108	109	261	144
Income (loss) from continuing operations		416	413	1,003	800
Property additions		326	391	993	1,115
Total assets		30,546		30,546		30,855
Goodwill		5,004		5,004		5,004
Operating Segments | Regulated Distribution | External Customers
Segment Financial Information
Revenues		2,708	2,611	7,237	7,062
Operating Segments | Regulated Distribution | Internal Customers
Segment Financial Information
Revenues		51	50	150	145
Operating Segments | Regulated Transmission
Segment Financial Information
Revenues		415	413	1,233	1,198
Depreciation		82	79	240	233
Amortization (deferral) of regulatory assets, net		1	0	12	6
DPA penalty (Note 9)				0
Miscellaneous income (expense), net		12	7	34	21
Interest expense		62	55	186	162
Income taxes (benefits)		23	35	93	103
Income (loss) from continuing operations		70	115	295	346
Property additions		202	278	732	817
Total assets		12,660		12,660		12,592
Goodwill		614		614		614
Operating Segments | Regulated Transmission | External Customers
Segment Financial Information
Revenues		411	408	1,223	1,185
Operating Segments | Regulated Transmission | Internal Customers
Segment Financial Information
Revenues		4	5	10	13
Corporate/Other
Segment Financial Information
Revenues		5	3	12	6
Depreciation		(1)	0	1	2
Amortization (deferral) of regulatory assets, net		0	0	0	0
DPA penalty (Note 9)				230
Miscellaneous income (expense), net		23	13	59	45
Interest expense		89	88	288	265
Income taxes (benefits)		(43)	(28)	(83)	(125)
Income (loss) from continuing operations		(70)	(68)	(489)	(355)
Property additions		14	18	43	47
Total assets		648		648		1,017
Goodwill		0		0		0
Corporate/Other | External Customers
Segment Financial Information
Revenues		5	3	12	6
Corporate/Other | Internal Customers
Segment Financial Information
Revenues		0	0	0	0
Reconciling Adjustments
Segment Financial Information
Revenues		(55)	(55)	(160)	(158)
Depreciation		16	14	47	47
Amortization (deferral) of regulatory assets, net		0	0	0	0
DPA penalty (Note 9)				0
Miscellaneous income (expense), net		(1)	(1)	(11)	(9)
Interest expense		(1)	(1)	(11)	(9)
Income taxes (benefits)		0	0	0	0
Income (loss) from continuing operations		0	0	0	0
Property additions		0	0	0	0
Total assets		0		0		0
Goodwill		0		0		$ 0
Reconciling Adjustments | External Customers
Segment Financial Information
Revenues		0	0	0	0
Reconciling Adjustments | Internal Customers
Segment Financial Information
Revenues		$ (55)	$ (55)	$ (160)	$ (158)

[1] Includes excise and gross receipts tax collections of $103 million and $100 million during the three months ended September 30, 2021 and 2020, respectively, and $283 million and $276 million during the nine months ended September 30, 2021 and 2020, respectively.