MISCELLANEOUS INCOME (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income and Expenses [Abstract]
Equity portion of AFUDC	$ 11.0wps_EquityPortionOfAFUDC	$ 9.9wps_EquityPortionOfAFUDC	$ 2.6wps_EquityPortionOfAFUDC
Earnings from equity method investments	10.3	11.3	11.0
Key executive life insurance for retired employees	1.6	1.1	1.1
Coal transportation services	1.0	1.2	0.9
Other	0.5wps_OtherNonoperatingIncomeExpenseOther	0wps_OtherNonoperatingIncomeExpenseOther	0.1wps_OtherNonoperatingIncomeExpenseOther
Total miscellaneous income	$ 24.4us-gaap_OtherNonoperatingIncomeExpense	$ 23.5us-gaap_OtherNonoperatingIncomeExpense	$ 15.7us-gaap_OtherNonoperatingIncomeExpense

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.12)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 7

+ Details

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- Details

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- Definition

The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.9)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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- Definition

Represents income related to the equity portion of AFUDC (allowance for funds used during construction).

+ References

No definition available.

+ Details

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- Definition

Represents the income associated with key executive life insurance for retired employees.

+ References

No definition available.

+ Details

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- Definition

Represent income earned from coal transportation services.

+ References

No definition available.

+ Details

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- Definition

The net amount of other income and expense amounts, the components of which are not separately stated in the disclosure for other nonoperating income and expenses.

+ References

No definition available.

+ Details

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