Summary of Significant Accounting Policies - SPPC - Property, Plant and Equipment, Net (Details) - Sierra Pacific Power Company [Member]	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Electricity Generation Plant, Non-Nuclear [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	6.65%	7.62%
Natural Gas Processing Plant [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	5.63%	6.02%
Common Facilities [Member]
Property, Plant and Equipment [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	6.55%	7.44%

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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Period Type:	duration