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Regulatory Matters - SPPC - Other (Details) - Sierra Pacific Power Company [Member] - Public Utilities Commission, Nevada [Member] - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Energy Efficiency Rate Case [Member]    
Public Utilities, General Disclosures [Line Items]    
Customer Refund Liability, Current $ 2 $ 3
Electric Distribution [Member] | General Rate Case [Member]    
Public Utilities, General Disclosures [Line Items]    
Public Utilities, Approved Rate Increase (Decrease), Amount 3  
Gas Distribution [Member] | General Rate Case [Member]    
Public Utilities, General Disclosures [Line Items]    
Public Utilities, Approved Rate Increase (Decrease), Amount $ 2