Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets and Liabilities [Line Items]
Employee benefits	$ 190	$ 187
Regulatory liabilities	834	812
Other	815	781
Total deferred income tax assets	3,104	2,872
Property-related items	(13,157)	(11,989)
Regulatory assets	(1,446)	(1,374)
Other	(299)	(301)
Total deferred income tax liabilities	(15,754)	(14,363)
Net deferred income tax liability	(12,685)	(11,514)
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal	39	56
Employee benefits	25	22
Regulatory liabilities	19	21
Deferred Tax Assets, Tax Deferred Expense, Leases	13	9
Deferred Tax Assets, Customer Advances	8	7
Other	12	15
Total deferred income tax assets	116	130
Property-related items	(538)	(478)
Regulatory assets	(121)	(147)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(13)	(9)
Other	(14)	(20)
Total deferred income tax liabilities	(686)	(654)
Net deferred income tax liability	$ (570)	$ (524)