COMMON EQUITY (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Common Equity
Total restricted net assets	$ 1,324.8
Equity in undistributed earnings of 50% or less owned investees accounted under equity method investments	28.8
Common stock dividends paid	54.3	52.8
Capital returned	35.0	0
Maximum
Common Equity
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
Ownership interest (as a percent)	50.00%
Maximum | Public Service Commission of Wisconsin (PSCW)
Common Equity
Percentage of previous period's dividend as restriction on current period dividends	103.00%
Minimum | Public Service Commission of Wisconsin (PSCW)
Common Equity
Common equity ratio required to be maintained (as a percent)	51.00%
Integrys Energy Group
Common Equity
Receipt of capital contribution	200.0
Common stock dividends paid	$ 54.3
Integrys Energy Group | Minimum
Common Equity
Percentage of common stockholders equity to total capitalization for dividend payment restrictions	25.00%