LONG-TERM DEBT (Details) - USD ($) $ in Millions	Aug. 01, 2015	Jul. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Total			$ 3,081.9	$ 3,081.9
Unamortized discount on debt			(0.6)	(0.6)
Total debt			3,081.3	3,081.3
Less current portion			180.0	125.0
Total long-term debt			2,901.3	2,956.3
WPS
Debt Instrument [Line Items]
Total			1,175.1	1,175.1
PGL
Debt Instrument [Line Items]
Total			850.0	850.0
NSG
Debt Instrument [Line Items]
Total			82.0	82.0
Integrys Holding
Debt Instrument [Line Items]
Total			$ 974.8	$ 974.8
Fixed First and Refunding Mortgage WW Series 2.625 Percent Bonds, Due 2033 | PGL
Debt Instrument [Line Items]
Interest rate stated percentage			2.625%
Unsecured Senior Notes 8.00 Percent, Due 2016 | Integrys Holding
Debt Instrument [Line Items]
Less current portion			$ 55.0
Subsequent event | Fixed First and Refunding Mortgage WW Series 2.625 Percent Bonds, Due 2033 | PGL
Debt Instrument [Line Items]
Total	$ 50.0
Interest rate stated percentage	1.875%
Subsequent event | Unsecured Senior Notes 8.00 Percent, Due 2016 | Integrys Holding
Debt Instrument [Line Items]
Interest rate stated percentage		8.00%
Offer to Buy Back $55 Million 8% Senior Notes Due 6/1/16		$ 55.0