Regulatory Matters - PAC - 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
Employee benefit plans
Regulatory Assets [Line Items]
Regulatory asset, amortization period	15 years
Total regulatory assets	$ 472	722
Deferred net power costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	1 year
Total regulatory assets	$ 531	139
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
Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory asset, amortization period	14 years
Total regulatory assets	$ 742	640
Demand side management
Regulatory Assets [Line Items]
Regulatory asset, amortization period	10 years
Total regulatory assets	$ 211	197
PAC
Regulatory Assets [Line Items]
Total regulatory assets	1,352	1,395
Regulatory assets, current	65	116
Regulatory assets, noncurrent	1,287	1,279
Regulatory assets not earning a return on investment	$ 723	707
PAC | DSM Regulatory Assets
Regulatory Assets [Line Items]
Amounts billed to customers, acceleration depreciation		185
PAC | Employee benefit plans
Regulatory Assets [Line Items]
Regulatory asset, amortization period	17 years
Total regulatory assets	$ 286	432
PAC | Utah mine disposition
Regulatory Assets [Line Items]
Total regulatory assets	$ 116	117
PAC | Unamortized contract values
Regulatory Assets [Line Items]
Regulatory asset, amortization period	2 years
Total regulatory assets	$ 36	42
PAC | Deferred net power costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	2 years
Total regulatory assets	$ 151	78
PAC | Unrealized loss on derivative contracts
Regulatory Assets [Line Items]
Total regulatory assets	$ 0	17
PAC | Environmental costs
Regulatory Assets [Line Items]
Regulatory asset, amortization period	28 years
Total regulatory assets	$ 108	89
PAC | Asset retirement obligations
Regulatory Assets [Line Items]
Regulatory asset, amortization period	29 years
Total regulatory assets	$ 241	252
PAC | Demand side management
Regulatory Assets [Line Items]
Regulatory asset, amortization period	10 years
Total regulatory assets	$ 211	196
PAC | Other
Regulatory Assets [Line Items]
Total regulatory assets	$ 203	$ 172