Summary of Significant Accounting Policies - SPPC - Income Taxes (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets and Liabilities [Line Items]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Federal statutory income tax rate	35.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017 [Member]
Deferred Tax Assets and Liabilities [Line Items]
Federal statutory income tax rate	21.00%
Tax Cuts and Jobs Act of 2017 [Member] | Sierra Pacific Power Company [Member]
Deferred Tax Assets and Liabilities [Line Items]
Federal statutory income tax rate	21.00%