Unaudited Quarterly Operating Results - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2014
Quarterly Operating Results [Line Items]
Electric Domestic Operating Revenue, Quarterly	$ 185	$ 228	$ 201	$ 196	$ 190	$ 179	$ 177	$ 233
Gas Domestic Operating Revenue, Quarterly	43	18	26	50	42	21	44	18
Operating Income (loss), Quarterly	38	66	37	43	41	31	46	60
Net Income (Loss) Attributable to Parent, Quarterly	$ 15	$ 33	$ 16	$ 19	$ 20	$ 14	$ 22	$ 31