Property Plant and Equipment Property Plant and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	$ 3,880	$ 3,674
Accumulated Depreciation	1,396	1,315
Property, Plant and Equipment, Net	2,484	2,359
Electric plant
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	3,197	3,025
Natural gas plant
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	391	365
Common and other property
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	221	201
CWIP
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	$ 71	$ 83