Revenues (Details) - Regulated Electric - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 488	$ 415	$ 1,408	$ 802
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	498	423	1,432	818
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	296	257	584	507
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	85	85	176	158
Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	201	164	389	333
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	8	19	16
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	118	82	676	155
Transmission
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72	76	143	139
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	0	5	1
Alternative and Other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 10	$ 8	$ 24	$ 16