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Commitments and Contingencies - SPPC - Commitments Table (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Contractual Obligation [Line Items]      
Contractual Obligation, Due in Next Twelve Months $ 5,048    
Contractual Obligation, Due in Second Year 2,767    
Contractual Obligation, Due in Third Year 1,895    
Contractual Obligation, Due in Fourth Year 1,590    
Contractual Obligation, Due in Fifth Year 1,399    
Contractual Obligation, Due after Fifth Year 14,251    
Contractual Obligation 26,950    
Fuel, capacity and transmission contract commitments [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 2,215    
Purchase Obligation, Due in Second Year 1,659    
Purchase Obligation, Due in Third Year 1,380    
Purchase Obligation, Due in Fourth Year 1,174    
Purchase Obligation, Due in Fifth Year 1,047    
Purchase Obligation, Due after Fifth Year 11,155    
Purchase Obligation 18,630    
Maintenance, service and other contracts [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 306    
Purchase Obligation, Due in Second Year 344    
Purchase Obligation, Due in Third Year 303    
Purchase Obligation, Due in Fourth Year 277    
Purchase Obligation, Due in Fifth Year 241    
Purchase Obligation, Due after Fifth Year 1,358    
Purchase Obligation 2,829    
Sierra Pacific Power Company [Member]      
Contractual Obligation [Line Items]      
Contractual Obligation, Due in Next Twelve Months 224    
Contractual Obligation, Due in Second Year 181    
Contractual Obligation, Due in Third Year 155    
Contractual Obligation, Due in Fourth Year 148    
Contractual Obligation, Due in Fifth Year 123    
Contractual Obligation, Due after Fifth Year 1,953    
Contractual Obligation 2,784    
Rent expense for power purchase agreements meeting definition of operating lease 72 $ 74 $ 69
Operating Lease and Easement, Expense 4 $ 4 $ 6
Sierra Pacific Power Company [Member] | Fuel, capacity and transmission contract commitments [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 204    
Purchase Obligation, Due in Second Year 154    
Purchase Obligation, Due in Third Year 117    
Purchase Obligation, Due in Fourth Year 81    
Purchase Obligation, Due in Fifth Year 61    
Purchase Obligation, Due after Fifth Year 502    
Purchase Obligation 1,119    
Sierra Pacific Power Company [Member] | Fuel, capacity and transmission contract commitments, Not commercially operable [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 8    
Purchase Obligation, Due in Second Year 16    
Purchase Obligation, Due in Third Year 28    
Purchase Obligation, Due in Fourth Year 58    
Purchase Obligation, Due in Fifth Year 58    
Purchase Obligation, Due after Fifth Year 1,394    
Purchase Obligation 1,562    
Sierra Pacific Power Company [Member] | Operating Leases, Easements, Maintenance and Service [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 4    
Purchase Obligation, Due in Second Year 4    
Purchase Obligation, Due in Third Year 4    
Purchase Obligation, Due in Fourth Year 3    
Purchase Obligation, Due in Fifth Year 2    
Purchase Obligation, Due after Fifth Year 56    
Purchase Obligation 73    
Sierra Pacific Power Company [Member] | Maintenance, service and other contracts [Member]      
Contractual Obligation [Line Items]      
Purchase Obligation, Due in Next Twelve Months 8    
Purchase Obligation, Due in Second Year 7    
Purchase Obligation, Due in Third Year 6    
Purchase Obligation, Due in Fourth Year 6    
Purchase Obligation, Due in Fifth Year 2    
Purchase Obligation, Due after Fifth Year 1    
Purchase Obligation $ 30