Fair Value Measurements - NPC - Level 3 (Details) - Nevada Power Company [Member] - Commodity [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (11)	$ (9)	$ 3	$ (3)
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net	13	(2)	30	6
Fair Value, Measurements With Unobservable Inputs Reconciliation, Recurring Basis, Assets and Liability, Net, Settlements	(6)	0	(9)	(2)
Ending balance	$ (18)	$ (7)	$ (18)	$ (7)