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Income Taxes Income Taxes - SPPC (Details)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Schedule of Effective Income Tax Rate Reconciliation [Line Items]          
Federal statutory income tax rate 21.00% 35.00% 21.00% 35.00% 35.00%
Effects of ratemaking (8.00%) (0.00%) (8.00%) (0.00%)  
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent (1.00%) 0.00% 1.00% 1.00%  
Effective income tax rate 86.00% (13.00%) 81.00% (11.00%)  
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% 21.00% 35.00% 35.00%
Effects of ratemaking (14.00%) (0.00%) 1.00% (0.00%)  
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 8.00% 0.00% 3.00% 0.00%  
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 3.00% 0.00% 0.00% 0.00%  
Effective income tax rate 46.00% 35.00% 23.00% 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%