Unaudited Quarterly Operating Results - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2016
Quarterly Operating Results [Line Items]
Electric Domestic Operating Revenue, Quarterly	$ 179	$ 215	$ 160	$ 159	$ 163	$ 162	$ 170	$ 207
Gas Domestic Operating Revenue, Quarterly	33	15	17	34	29	19	47	15
Operating Income (loss), Quarterly	41	75	36	46	42	28	41	69
Net Income (Loss) Attributable to Parent, Quarterly	$ 24	$ 44	$ 17	$ 24	$ 19	$ 10	$ 17	$ 38