Joint Ownership of Transmission Facilities (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Jointly Owned Utility Plant [Abstract]
Plant in service	$ 162,108
Accumulated depreciation	12,205
Construction work in progress	204,690
CapX2020 Transmission \| Electric Transmission
Jointly Owned Utility Plant [Abstract]
Plant in service	162,108
Accumulated depreciation	12,205
Construction work in progress	$ 103,144
Ownership % (in hundredths)	81.00%
La Crosse, Wis. to Madison, Wis. \| Electric Transmission
Jointly Owned Utility Plant [Abstract]
Plant in service	$ 0
Accumulated depreciation	0
Construction work in progress	$ 101,546
Ownership % (in hundredths)	37.00%

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

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

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- References

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

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- Definition

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

+ References

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