RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 ATC	Sep. 30, 2012 ATC	Sep. 30, 2013 ATC	Sep. 30, 2012 ATC	Dec. 31, 2012 ATC	Sep. 30, 2013 WRPC	Sep. 30, 2012 WRPC	Sep. 30, 2013 WRPC	Sep. 30, 2012 WRPC	Sep. 30, 2013 WPS Investments, LLC	Sep. 30, 2012 WPS Investments, LLC	Sep. 30, 2013 WPS Investments, LLC	Sep. 30, 2012 WPS Investments, LLC	Sep. 30, 2013 Integrys Energy Group	Dec. 31, 2012 Integrys Energy Group	Sep. 30, 2013 UPPCO Electric Utility	Sep. 30, 2012 UPPCO Electric Utility	Sep. 30, 2013 UPPCO Electric Utility	Sep. 30, 2012 UPPCO Electric Utility	Sep. 30, 2013 Integrys Energy Services Natural gas transactions	Sep. 30, 2012 Integrys Energy Services Natural gas transactions	Sep. 30, 2013 Integrys Energy Services Natural gas transactions	Sep. 30, 2012 Integrys Energy Services Natural gas transactions	Sep. 30, 2013 WPS Leasing Integrys Energy Group	Sep. 30, 2012 WPS Leasing Integrys Energy Group	Sep. 30, 2013 WPS Leasing Integrys Energy Group	Sep. 30, 2012 WPS Leasing Integrys Energy Group	Dec. 31, 2012 WPS Leasing Integrys Energy Group
RELATED PARTY TRANSACTIONS
Long-term debt to parent	$ 6.6		$ 7.2																								$ 6.6		$ 6.6		$ 7.2
Accounts payable to related parties				10.1		10.1		9.2
Liability related to income tax allocation																	6.9	7.4
Amount repaid to related parties	0	22.6	22.6
Sales to related party									0.2	0.2	0.7	0.6							6.4	6.1	17.7	17.1	0.1	0.1	0.3	0.5
Purchases from related party									1.0	1.2	3.0	3.7											0.2	0.1	0.6	0.5
Interest expense																											0.1	0.1	0.4	0.4
Charges from equity method investee for network transmission services				24.6	23.5	73.8	70.6
Charges to equity method investee for services and construction				1.9	1.8	6.0	6.9
Net proceeds from equity method investee's sales of energy to MISO									0	0.6	0	2.4
Income from equity method investee													$ 2.5	$ 2.5	$ 7.6	$ 7.6
Equity method investment, ownership interest (as a percent)													11.44%		11.44%