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Asset Retirement Obligations - NPC - Change in Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance $ 1,272 $ 985
Asset Retirement Obligation, Revision of Estimate 46 257
Retirements (201) (61)
Charge related to a voluntary retirement program 51 48
Ending Balance 1,341 1,272
Asset Retirement Obligation, Current 184 167
Asset Retirement Obligations, Noncurrent 1,157 1,105
Nevada Power Company [Member]    
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]    
Beginning Balance 74 83
Asset Retirement Obligation, Revision of Estimate 9 6
Retirements (14) (19)
Charge related to a voluntary retirement program 3 4
Ending Balance 72 74
Asset Retirement Obligation, Current 25 14
Asset Retirement Obligations, Noncurrent $ 47 $ 60