Utility Plant and Nonutility Property - Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Gross nonutility property	$ 45	$ 75
Generation
Property Plant And Equipment [Line Items]
Utility plant in service	5,921	5,765
Transmission
Property Plant And Equipment [Line Items]
Utility plant in service	1,963	1,905
Distribution
Property Plant And Equipment [Line Items]
Utility plant in service	4,909	4,685
Storage
Property Plant And Equipment [Line Items]
Utility plant in service	74	73
General and other
Property Plant And Equipment [Line Items]
Utility plant in service	563	549
Intangible
Property Plant And Equipment [Line Items]
Utility plant in service	250	231
Construction Work In Progress
Property Plant And Equipment [Line Items]
Utility plant in service	460	339
Nuclear Fuel
Property Plant And Equipment [Line Items]
Utility plant in service	575	608
Total Gross Utility Plant
Property Plant And Equipment [Line Items]
Utility plant in service	$ 14,715	$ 14,155