Risk Management and Hedging Activities - NPC - Derivative Contract Volumes (Details) - NPC - Commodity derivatives MWh in Millions, Dth in Millions	Dec. 31, 2021 Dth MWh	Dec. 31, 2020 MWh Dth
Electricity purchases (sales), net
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | MWh	1	1
Natural gas purchases
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, nonmonetary notional amount | Dth	119	124