Property, Plant and Equipment (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		$ 23,428	$ 22,896
Accumulated depreciation and amortization		(8,106)	(7,898)
Property, plant and equipment, net		15,679	15,308
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		19,647	18,948
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		1,720	1,707
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		969	955
Plant to be Retired (a)
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	[1]	127	136
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		965	1,150
Nuclear fuel
Public Utility, Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross		3,047	2,970
Accumulated depreciation and amortization		$ (2,690)	$ (2,660)

[1] Includes regulator-approved retirements of Sherco Units 1 and 2.