Subsidiary Debt Subsidiary Debt - SPPC (Details) - Sierra Pacific Power Company [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Equipment [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	7 years
Capital Leased Assets, Gross	$ 3	$ 3
ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	41 years
Capital Leased Assets, Gross	$ 21	21
Utilities Aggregate Share Transmission Line Project	25.00%
Remaining Share Transmission Line Project	75.00%
Solar Generating Facility [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	20 years
Capital Leased Assets, Gross	$ 9	$ 10
Sierra Pacific Power Company [Member] | ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Utilities Aggregate Share Transmission Line Project	5.00%
Nevada Power Company [Member] | ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Utilities Aggregate Share Transmission Line Project	95.00%