Subsidiary Debt Subsidiary Debt - NPC - (Details) - Nevada Power Company [Member] $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) option	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Eligible Property Subject To Lien Of Mortgages	$ 8,700
Building [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	30 years
Renewal Options Under Capital Lease, Number | option	5
Number Of Years In Renewal Period	5 years
Number Of Renewal Options Exercised Under Capital Lease | option	3
Number Of Additional Renewal Options Under Capital Lease | option	2
Extended Additional Term Of Capital Lease	10 years
Capital Leased Assets, Gross	$ 27	$ 28
Land and Building [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	20 years
Renewal Options Under Capital Lease, Number | option	3
Number Of Years In Renewal Period	10 years
Capital Leased Assets, Gross	$ 7	8
Long-Term Energy Purchase Contracts [Member]
Debt Instrument [Line Items]
Number Of Years In Renewal Period	30 years
Capital Leased Assets, Gross	$ 40	44
Equipment [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	7 years
Capital Leased Assets, Gross		1
ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Terms Of Capital Lease	41 years
Capital Leased Assets, Gross	$ 410	$ 418
Utilities Aggregate Share Transmission Line Project	25.00%
Remaining Share Transmission Line Project	75.00%
Nevada Power Company [Member] | ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Utilities Aggregate Share Transmission Line Project	95.00%
Sierra Pacific Power Company [Member] | ON Line Transmission Line [Member]
Debt Instrument [Line Items]
Utilities Aggregate Share Transmission Line Project	5.00%