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Asset Retirement Obligations Asset Retirement Obligations - NPC - 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
Asset Retirement Obligation, Liabilities Incurred 25 59
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
Nevada Power Company [Member]    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance 85 86
Asset Retirement Obligation, Revision of Estimate 4 3
Asset Retirement Obligation, Liabilities Incurred 0 3
Retirements (10) (11)
Asset Retirement Obligation, Accretion Expense 4 4
Ending Balance 83 85
Asset Retirement Obligation, Current 20 13
Asset Retirement Obligations, Noncurrent $ 63 $ 72