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Jointly Owned Utility Facilities - SPPC (Details)
$ in Millions
Dec. 31, 2018
USD ($)
Jointly Owned Utility Plant Interests [Line Items]  
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 9,874
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 4,608
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress 134
Sierra Pacific Power Company [Member]  
Jointly Owned Utility Plant Interests [Line Items]  
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service 401
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 255
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress $ 1
Sierra Pacific Power Company [Member] | Valmy [Member]  
Jointly Owned Utility Plant Interests [Line Items]  
Jointly Owned Utility Plant, Proportionate Ownership Share 50.00%
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 389
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 252
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress $ 1
Sierra Pacific Power Company [Member] | ON Line Transmission Line [Member]  
Jointly Owned Utility Plant Interests [Line Items]  
Jointly Owned Utility Plant, Proportionate Ownership Share 1.00%
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 8
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 1
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress $ 0
Sierra Pacific Power Company [Member] | Valmy Transmission Line [Member]  
Jointly Owned Utility Plant Interests [Line Items]  
Jointly Owned Utility Plant, Proportionate Ownership Share 50.00%
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 4
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation 2
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress $ 0