Unaudited Quarterly Operating Results - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	3 Months Ended							9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017
Quarterly Operating Results [Line Items]
Electric Domestic Operating Revenue, Quarterly	$ 177	$ 225	$ 169	$ 181	$ 179	$ 160	$ 159	$ 215
Gas Domestic Operating Revenue, Quarterly	29	14	19	41	33	17	34	15
Operating Income (loss), Quarterly	30	56	19	47	41	36	46	75
Net Income (Loss) Attributable to Parent, Quarterly	$ 16	$ 35	$ 7	$ 34	$ 24	$ 17	$ 24	$ 44