Revenues (Details) - Regulated Electric - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 564	$ 537	$ 1,972	$ 1,339
Total revenues
Disaggregation of Revenue [Line Items]
Total revenues	575	615	2,007	1,434
Retail
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	378	353	963	860
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	126	121	302	278
Retail | C&I
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	241	219	631	552
Retail | Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	13	30	30
Wholesale
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	109	109	785	264
Transmission
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	75	74	218	212
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	6	3
Alternative and Other
Disaggregation of Revenue [Line Items]
Alternative revenue and other	$ 11	$ 78	$ 35	$ 95