Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets and Liabilities [Line Items]
Employee benefits	$ 209	$ 190
Regulatory liabilities	909	834
Derivative contracts	29	83
Other	707	815
Total deferred income tax assets	3,167	3,104
Property-related items	(14,237)	(13,157)
Regulatory assets	(1,449)	(1,446)
Other	(334)	(299)
Total deferred income tax liabilities	(16,982)	(15,754)
Net deferred income tax liability	(13,879)	(12,685)
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal	25	39
Employee benefits	22	25
Regulatory liabilities	16	19
Deferred Tax Assets, Tax Deferred Expense, Leases	12	13
Deferred Tax Assets, Customer Advances	9	8
Derivative contracts	5	5
Other	6	7
Total deferred income tax assets	95	116
Property-related items	(562)	(538)
Regulatory assets	(124)	(121)
Deferred Tax Liabilities, Tax Deferred Expense, Leases	(12)	(13)
Other	(14)	(14)
Total deferred income tax liabilities	(712)	(686)
Net deferred income tax liability	$ (617)	$ (570)