Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 2,577	$ 2,658	$ 5,718	$ 5,609
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,463	2,545	5,503	5,370
Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,145	2,172	4,813	4,619
Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	816	844	2,047	1,930
Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,297	1,293	2,701	2,619
Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	32	35	65	70
Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	154	194	343	382
Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	127	132	258	255
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	37	47	89	114
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues	114	113	215	239
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	2,148	2,267	4,385	4,449
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,856	1,917	3,755	3,749
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	624	678	1,351	1,365
Regulated Electric | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1,201	1,206	2,341	2,318
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	31	33	63	66
Regulated Electric | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	154	194	343	382
Regulated Electric | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	127	132	258	255
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	11	24	29	63
Regulated Electric | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues	101	81	189	168
Regulated Natural Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	298	262	1,082	887
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	272	239	1,022	836
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	182	157	677	547
Regulated Natural Gas | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	90	82	345	289
Regulated Natural Gas | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Regulated Natural Gas | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Regulated Natural Gas | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	26	23	60	51
Regulated Natural Gas | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues	10	30	20	67
All Other | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	17	16	36	34
All Other | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	17	16	36	34
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	10	9	19	18
All Other | Retail | C&I
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	6	5	15	12
All Other | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	1	2	2	4
All Other | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
All Other | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
All Other | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	0	0	0	0
All Other | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues	3	2	6	4
Total revenues
Disaggregation of Revenue [Line Items]
Total operating revenues	2,577	2,658	5,718	5,609
Total revenues | Regulated Electric
Disaggregation of Revenue [Line Items]
Total operating revenues	2,249	2,348	4,574	4,617
Total revenues | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	308	292	1,102	954
Total revenues | All Other
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 20	$ 18	$ 42	$ 38