Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 9,841	$ 9,691
Accumulated depreciation		(2,144)	(2,088)
Property, plant and equipment, net		7,697	7,603
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		9,293	9,229
Plant to be Retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	313	316
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 235	$ 146

[1] Includes expected retirement of Tolk and conversion of Harrington to natural gas.