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Income Taxes Income Taxes - SPPC (Details)
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Schedule of Effective Income Tax Rate Reconciliation [Line Items]      
Federal statutory income tax rate 21.00% 35.00% 35.00%
Effects of ratemaking (8.00%) (1.00%)  
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 1.00% 0.00%  
Effective income tax rate 78.00% (9.00%)  
Tax Cuts and Jobs Act of 2017 [Member]      
Schedule of Effective Income Tax Rate Reconciliation [Line Items]      
Federal statutory income tax rate 21.00%    
Sierra Pacific Power Company [Member]      
Schedule of Effective Income Tax Rate Reconciliation [Line Items]      
Federal statutory income tax rate 21.00% 35.00% 35.00%
Effects of ratemaking 5.00% (0.00%)  
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent (1.00%) 0.00%  
Effective income tax rate 15.00% 35.00%  
Sierra Pacific Power Company [Member] | Tax Cuts and Jobs Act of 2017 [Member]      
Schedule of Effective Income Tax Rate Reconciliation [Line Items]      
Federal statutory income tax rate 21.00%