Unaudited Quarterly Operating Results - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015
Quarterly Operating Results [Line Items]
Electric Domestic Operating Revenue, Quarterly	$ 163	$ 207	$ 162	$ 170	$ 185	$ 201	$ 196	$ 228
Gas Domestic Operating Revenue, Quarterly	29	15	19	47	43	26	50	18
Operating Income (loss), Quarterly	42	69	28	41	38	37	43	66
Net Income (Loss) Attributable to Parent, Quarterly	$ 19	$ 38	$ 10	$ 17	$ 15	$ 16	$ 19	$ 33