Fair Value Measurements - NPC - Level 3 (Details) - Nevada Power Company [Member] - Commodity [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (44)	$ (11)	$ (8)	$ 3
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net	(13)	13	31	30
Fair Value, Measurements With Unobservable Inputs Reconciliation, Recurring Basis, Assets and Liability, Net, Settlements	(31)	(6)	(39)	(9)
Ending balance	$ 0	$ (18)	$ 0	$ (18)