Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 328	$ 281
Regulated Electric | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	250	224
Regulated Natural Gas | Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	78	57
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	275	230
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	123	102
Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	150	126
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2
Retail | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	199	175
Retail | Regulated Electric | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	81	71
Retail | Regulated Electric | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	116	102
Retail | Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	2
Retail | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	76	55
Retail | Regulated Natural Gas | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	42	31
Retail | Regulated Natural Gas | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34	24
Retail | Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Interchange
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	46
Interchange | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	46
Interchange | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1
Other | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0
Other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	324	277
Total revenue from contracts with customers | Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	247	221
Total revenue from contracts with customers | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	77	56
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	4	4
Alternative revenue and other | Regulated Electric
Disaggregation of Revenue [Line Items]
Alternative revenue and other	3	3
Alternative revenue and other | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 1	$ 1