Jointly-Owned Facilities and Projects (Details) $ in Millions	Dec. 31, 2015 USD ($) MW	Dec. 31, 2014 USD ($)
Jointly-Owned Facilities and Projects [Line Items]
Plant in Service	$ 769.3	$ 474.6
Accumulated Depreciation	198.4	210.8
Construction Work in Progress	$ 6.9	212.1
CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	3
Completed Project - Prior Years [Member] \| CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	2
Transmission [Member] \| CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Plant in Service	$ 101.1	55.5
Accumulated Depreciation	3.4	1.7
Construction Work in Progress	$ 0.0	$ 44.0
Transmission [Member] \| CapX2020 Projects [Member] \| Minimum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	9.30%	9.30%
Transmission [Member] \| CapX2020 Projects [Member] \| Maximum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	14.70%	14.70%
Transmission [Member] \| Completed Project - Current Year [Member] \| CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	1
Transmission [Member] \| Completed Project - Prior Years [Member] \| CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	2
Boswell Unit 4 [Member] \| Generation [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	80.00%	80.00%
Generating Capacity (MW) \| MW	585
% Not Owned	20.00%
Plant in Service	$ 668.2	$ 419.1
Accumulated Depreciation	195.0	209.1
Construction Work in Progress	$ 6.9	$ 168.1

Capacity of a generating facility, unit, or project in megawatts.

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- Definition

Jointly-Owned Electric Facility Percentage Not Owned

+ References

No definition available.

+ Details

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- Definition

Number of projects.

+ References

No definition available.

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- Definition

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

+ References

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

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ 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.

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