Commitments and Contingencies - SPPC - Legal (Details)	Dec. 31, 2015
Idaho Power Company [Member] \| Valmy Generating Station [Member]
Loss Contingencies [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%

The proportionate share of interest (percent) in a jointly owned utility plant.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 10.C)
-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 10
-Section C

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant