Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 274	$ 251	$ 810	$ 726
Regulated Electric | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	252	236	700	647
Regulated Natural Gas | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	22	15	110	79
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	221	204	656	588
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	81	78	262	238
Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	138	125	387	345
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	7	5
Retail | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	201	191	551	513
Retail | Regulated Electric | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	73	71	208	195
Retail | Regulated Electric | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	126	119	336	313
Retail | Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	7	5
Retail | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	20	13	105	75
Retail | Regulated Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	7	54	43
Retail | Regulated Natural Gas | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	6	51	32
Retail | Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Interchange
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48	41	140	123
Interchange | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	48	41	140	123
Interchange | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2	4	4
Other | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	0	1
Other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	4	3
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	271	247	800	715
Total revenue from contracts with customers | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	249	233	691	637
Total revenue from contracts with customers | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	14	109	78
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	3	4	10	11
Alternative revenue and other | Regulated Electric
Disaggregation of Revenue [Line Items]
Alternative revenue and other	3	3	9	10
Alternative revenue and other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 0	$ 1	$ 1	$ 1