Utility Plant and Nonutility Property - Property, Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Gross nonutility property	$ 75	$ 73
Generation
Property Plant And Equipment [Line Items]
Utility plant in service	5,765	5,751
Transmission
Property Plant And Equipment [Line Items]
Utility plant in service	1,905	1,758
Distribution
Property Plant And Equipment [Line Items]
Utility plant in service	4,685	4,456
Storage
Property Plant And Equipment [Line Items]
Utility plant in service	73	74
General and other
Property Plant And Equipment [Line Items]
Utility plant in service	549	535
Intangible
Property Plant And Equipment [Line Items]
Utility plant in service	231	229
Construction Work In Progress
Property Plant And Equipment [Line Items]
Utility plant in service	339	350
Nuclear Fuel
Property Plant And Equipment [Line Items]
Utility plant in service	608	611
Total Gross Utility Plant
Property Plant And Equipment [Line Items]
Utility plant in service	$ 14,155	$ 13,764