Revenues (Details) - Regulated Electric - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 920	$ 386
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	934	395
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	289	250
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	91	73
Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	189	169
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	558	73
Transmission
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	71	63
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	0
Alternative and Other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 14	$ 9