PREFERRED STOCK (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Preferred stock
Authorized shares	1,000,000us-gaap_PreferredStockSharesAuthorized
Mandatorily redeemable shares	0
Par value (in dollars per share)	$ 100
Shares outstanding	511,882us-gaap_PreferredStockSharesOutstanding	511,882us-gaap_PreferredStockSharesOutstanding
Carrying value	$ 51.2us-gaap_PreferredStockValue	$ 51.2us-gaap_PreferredStockValue
Notice period for redemption of preferred stock	30 days
Pre-emptive, subscription, or conversion rights	0
Sinking fund provisions	0wps_SinkingFundProvisions
5.00% preferred stock series
Preferred stock
Series (as a percent)	5.00%
Shares outstanding	131,916	131,916
Carrying value	13.2	13.2
5.04% preferred stock series
Preferred stock
Series (as a percent)	5.04%
Shares outstanding	29,983	29,983
Carrying value	3.0	3.0
5.08% preferred stock series
Preferred stock
Series (as a percent)	5.08%
Shares outstanding	49,983	49,983
Carrying value	5.0	5.0
6.76% preferred stock series
Preferred stock
Series (as a percent)	6.76%
Shares outstanding	150,000	150,000
Carrying value	15.0	15.0
6.88% preferred stock series
Preferred stock
Series (as a percent)	6.88%
Shares outstanding	150,000	150,000
Carrying value	$ 15.0	$ 15.0

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The percentage rate used to calculate dividend payments on preferred stock.

+ References

No definition available.

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- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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- Definition

The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

+ References

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- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ References

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- Definition

Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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- Definition

Number of preferred stock shares that are mandatorily redeemable.

+ References

No definition available.

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- Definition

Number of pre-emptive, subscription, or conversion rights on preferred stock.

+ References

No definition available.

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- Definition

Notice period for the redemption of preferred stock that is redeemable in whole or in part at WPS's option.

+ References

No definition available.

+ Details

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- Definition

Number of sinking fund provisions on preferred stock.

+ References

No definition available.

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