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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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The distributions of earnings to an entity that is affiliated with the reporting entity by means of direct or indirect ownership.

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The cash inflow from an entity that is affiliated with the entity by means of direct or indirect ownership.

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A segregation of retained earnings which is unavailable for dividend distribution. Includes also retained earnings appropriated for loss contingencies.

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Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50% or less owned persons accounted for by the equity method (equity method investees).

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Represents the common equity ratio which is required to be maintained.

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Represents the percentage of common stockholders equity to total capitalization for dividend payment restrictions.

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Represents the maximum debt to capitalization ratio.

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Represents the percentage of previous period's dividend as restriction on current period's dividends.

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COMMON EQUITY (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividend Payment Restrictions
Maximum debt to capitalization ratio required to be maintained (as a percent)	65.00%wps_MaximumDebttoCapitalizationRatio
Total restricted retained earnings	$ 521.8us-gaap_RetainedEarningsAppropriated
Equity in undistributed earnings of 50% or less owned investees accounted for by the equity method	30.8
Capital Transactions with Parent
Common stock dividends paid	111.8	108.6	105.5
Minimum
Dividend Payment Restrictions
Percentage of common stockholders equity to total capitalization required to be maintained	25.00%
Minimum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Common equity ratio required to be maintained (as a percent)	51.00%
Maximum
Dividend Payment Restrictions
Equity method investment, ownership interest (as a percent)	50.00%
Maximum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Percentage of previous year's dividend as restriction on current year dividends	103.00%
Integrys Energy Group
Capital Transactions with Parent
Receipt of capital contribution	55.0
Common stock dividends paid	$ 111.8