Regulatory Matters - Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Total regulatory assets	$ 3,963	$ 3,440
Regulatory assets, current	544	283
Regulatory assets, noncurrent	3,419	3,157
Regulatory assets not earning a return on investment	$ 1,800	1,600
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory asset, amortization period	14 years
Total regulatory assets	$ 742	640
Deferred net power costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 531	139
Employee benefit plans
Regulatory Assets [Line Items]
Regulatory asset, amortization period	15 years
Total regulatory assets	$ 472	722
Deferred income taxes
Regulatory Assets [Line Items]
Total regulatory assets	342	283
Asset disposition costs
Regulatory Assets [Line Items]
Total regulatory assets	$ 285	347
Demand side management
Regulatory Assets [Line Items]
Regulatory asset, amortization period	10 years
Total regulatory assets	$ 211	197
Unrealized loss on derivative contracts
Regulatory Assets [Line Items]
Total regulatory assets	$ 157	31
Environmental costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	28 years
Total regulatory assets	$ 108	89
Deferred operating costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	9 years
Total regulatory assets	$ 103	124
Other
Regulatory Assets [Line Items]
Total regulatory assets	$ 1,012	$ 868