Fair Value Measurements - NPC - Level 3 (Details) - Commodity [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Net, Value	$ 99	$ 94	$ 60	$ 47
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net	(3)	1	11
Settlements	4	(14)	(17)
Ending balance	99	94	60
Nevada Power Company [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability), Net, Value	3	(3)	(14)	$ (22)
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net	4	(3)	(4)
Settlements	2	14	12
Ending balance	$ 3	$ (3)	$ (14)