COMMON EQUITY (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012
Dividend Payment Restrictions
Total restricted net assets	$ 1,313.2
Equity in undistributed earnings of 50% or less owned investees accounted under equity method investments	28.9
Capital Transactions with Parent
Common stock dividends paid	81.5	79.1
Capital returned	35.0	50.0
Maximum
Dividend Payment Restrictions
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
Equity method investment, ownership interest (as a percent)	50.00%
Maximum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Percentage of previous period's dividend as restriction on current period dividends	103.00%
Minimum \| Public Service Commission of Wisconsin (PSCW)
Dividend Payment Restrictions
Common equity ratio required to be maintained (as a percent)	51.00%
Integrys Energy Group
Capital Transactions with Parent
Receipt of capital contribution	200.0
Common stock dividends paid	81.5
Capital returned	$ 35.0
Integrys Energy Group \| Minimum
Dividend Payment Restrictions
Percentage of common stockholders equity to total capitalization for dividend payment restrictions	25.00%

Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year.

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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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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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