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Asset Retirement Obligations - SPPC - Change in Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 921 $ 753
Asset Retirement Obligation, Revision of Estimate 33 104
Retirements (63) (32)
Asset Retirement Obligation, Accretion Expense 38 37
Ending Balance 954 921
Asset Retirement Obligation, Current 98 92
Asset Retirement Obligations, Noncurrent 856 829
Sierra Pacific Power Company [Member]    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance 10 11
Retirements 0 (1)
Ending Balance 10 10
Asset Retirement Obligation, Current 0 0
Asset Retirement Obligations, Noncurrent $ 10 $ 10