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Asset Retirement Obligations - SPPC - Change in Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 753 $ 696
Asset Retirement Obligation, Revision of Estimate 104 3
Retirements (32) (8)
Asset Retirement Obligation, Accretion Expense 37 35
Ending Balance 921 753
Asset Retirement Obligation, Current 92 66
Asset Retirement Obligations, Noncurrent 829 687
Sierra Pacific Power Company [Member]    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance 11 16
Asset Retirement Obligation, Revision of Estimate 0 (6)
Retirements (1) 0
Asset Retirement Obligation, Accretion Expense 0 1
Ending Balance 10 11
Asset Retirement Obligation, Current 0 3
Asset Retirement Obligations, Noncurrent $ 10 $ 8