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Income Taxes - SPPC - Components of Net Deferred Income Tax Liability (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Deferred Tax Assets and Liabilities [Line Items]    
Regulatory liabilities $ 1,707 $ 909
Employee benefits 45 209
Derivative contracts 2 29
Other 448 707
Total deferred income tax assets 3,543 3,167
Property-related items (9,950) (14,237)
Regulatory assets (651) (1,449)
Other (215) (334)
Total deferred income tax liabilities (11,659) (16,982)
Net deferred income tax liability (8,242) (13,879)
Sierra Pacific Power Company [Member]    
Deferred Tax Assets and Liabilities [Line Items]    
Regulatory liabilities 67 16
Deferred Tax Assets, Operating Loss and Credit Carryforwards, Federal 10 25
Employee benefits 10 22
Deferred Tax Assets, Tax Deferred Expense, Leases 7 12
Deferred Tax Assets, Customer Advances 7 9
Derivative contracts 0 5
Other 6 6
Total deferred income tax assets 107 95
Property-related items (349) (562)
Regulatory assets (74) (124)
Deferred Tax Liabilities, Tax Deferred Expense, Leases (7) (12)
Other (7) (14)
Total deferred income tax liabilities (437) (712)
Net deferred income tax liability $ (330) $ (617)