Fair Value Measurements Fair Value Measurements - SPPC - Level 3 (Details) - Sierra Pacific Power Company [Member] - Commodity [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets (Liabilities), Net, Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (2)	$ 0	$ 0	$ 0
Fair Value, Measurements with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included In Regulatory Assets and Liabilities, Net	2	0	(1)	0
Settlements	(1)	0	0	0
Ending balance	$ (1)	$ 0	$ (1)	$ 0