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Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Regulatory Assets [Line Items]    
Regulatory Assets $ 3,440 $ 2,881
Regulatory Assets, Current 283 115
Regulatory Assets, Noncurrent 3,157 2,766
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided 1,600 1,400
Deferred Operating Costs    
Regulatory Assets [Line Items]    
Regulatory Assets 124 134
Sierra Pacific Power Company [Member]    
Regulatory Assets [Line Items]    
Regulatory Assets 334 295
Regulatory Assets, Current 67 12
Regulatory Assets, Noncurrent 267 283
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided $ 149 168
Sierra Pacific Power Company [Member] | Employee benefit plans    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period [1] 8 years  
Regulatory Assets [1] $ 81 107
Sierra Pacific Power Company [Member] | Merger costs from 1999 merger    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 26 years  
Regulatory Assets $ 68 71
Sierra Pacific Power Company [Member] | Natural Disaster Protection Plan    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 1 year  
Regulatory Assets $ 45 8
Sierra Pacific Power Company [Member] | Deferred Operating Costs    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 11 years  
Regulatory Assets $ 27 23
Sierra Pacific Power Company [Member] | Abandoned projects    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 6 years  
Regulatory Assets $ 22 24
Sierra Pacific Power Company [Member] | Deferred energy costs    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 1 year  
Regulatory Assets $ 22 4
Sierra Pacific Power Company [Member] | Losses on reacquired debt    
Regulatory Assets [Line Items]    
Regulatory Asset, Amortization Period 15 years  
Regulatory Assets $ 15 17
Sierra Pacific Power Company [Member] | Other    
Regulatory Assets [Line Items]    
Regulatory Assets $ 54 $ 41
[1] Represents amounts not yet recognized as a component of net periodic benefit cost that are expected to be included in regulated rates when recognized.