Jointly-Owned Facilities and Projects (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Jointly-Owned Facilities and Projects [Line Items]
Plant in Service	$ 438.9
Accumulated Depreciation	198.5
Construction Work in Progress	129.2
Boswell Unit 4 [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	80.00%
Generating Capacity (MW)	585
% Not Owned	20.00%
Plant in Service	416.1
Accumulated Depreciation	197.5
Construction Work in Progress	71.5
CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	3
Plant in Service	22.8
Accumulated Depreciation	1.0
Construction Work in Progress	$ 57.7
CapX2020 Projects [Member] \| Minimum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	9.30%
CapX2020 Projects [Member] \| Maximum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	14.70%

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

No definition available.

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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.

+ Details

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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

+ Details

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- Definition

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

+ References

+ Details

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- Definition

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

+ References

+ Details

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- Definition

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

+ References

+ Details

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