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Asset Retirement Obligations - SPPC - Change in Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 954 $ 954
Retirements (45) (45)
Ending Balance 985 954
Asset Retirement Obligation, Current 43 60
Asset Retirement Obligations, Noncurrent 942 894
Sierra Pacific Power Company [Member]    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance 10 10
Retirements 0 0
Ending Balance 10 10
Asset Retirement Obligation, Current 0 0
Asset Retirement Obligations, Noncurrent $ 10 $ 10