Revenues (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,352	$ 1,250
Regulated Electric \| Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	1,139	1,035
Regulated Natural Gas \| Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	204	206
All Other \| Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	9	9
Retail
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	952	957
Retail \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	447	421
Retail \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	495	527
Retail \| Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	10	9
Retail \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	750	752
Retail \| Regulated Electric \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	326	300
Retail \| Regulated Electric \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	416	445
Retail \| Regulated Electric \| Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	8	7
Retail \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	193	196
Retail \| Regulated Natural Gas \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	114	114
Retail \| Regulated Natural Gas \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	79	82
Retail \| Regulated Natural Gas \| Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Retail \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9	9
Retail \| All Other \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	7	7
Retail \| All Other \| C&I
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Retail \| All Other \| Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2	2
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	98	45
Wholesale \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	98	45
Wholesale \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Wholesale \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Transmission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	57	56
Transmission \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	57	56
Transmission \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Transmission \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Interchange
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	115	110
Interchange \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	115	110
Interchange \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Interchange \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2	3
Other \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2	2
Other \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	1
Other \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0	0
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,224	1,171
Total revenue from contracts with customers \| Regulated Electric
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1,022	965
Total revenue from contracts with customers \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	193	197
Total revenue from contracts with customers \| All Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9	9
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	128	79
Alternative revenue and other \| Regulated Electric
Disaggregation of Revenue [Line Items]
Alternative revenue and other	117	70
Alternative revenue and other \| Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Alternative revenue and other	11	9
Alternative revenue and other \| All Other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 0	$ 0

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