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Fair Value Measurements - NPC - Level 3 (Details) - Nevada Power Company [Member] - Commodity [Member] - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Beginning balance $ (38) $ (5) $ (8) $ 3
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net 13 8 44 17
Fair Value, Measurements With Unobservable Inputs Reconciliation, Recurring Basis, Assets and Liability, Net, Settlements (7) (2) (8) (3)
Ending balance $ (44) $ (11) $ (44) $ (11)