RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 ATC	Jun. 30, 2012 ATC	Jun. 30, 2013 ATC	Jun. 30, 2012 ATC	Dec. 31, 2012 ATC	Jun. 30, 2013 WRPC	Jun. 30, 2012 WRPC	Jun. 30, 2013 WRPC	Jun. 30, 2012 WRPC	Jun. 30, 2013 WPS Investments, LLC	Jun. 30, 2012 WPS Investments, LLC	Jun. 30, 2013 WPS Investments, LLC	Jun. 30, 2012 WPS Investments, LLC	Jun. 30, 2013 Integrys Energy Group	Dec. 31, 2012 Integrys Energy Group	Jun. 30, 2013 UPPCO Electric Utility	Jun. 30, 2012 UPPCO Electric Utility	Jun. 30, 2013 UPPCO Electric Utility	Jun. 30, 2012 UPPCO Electric Utility	Jun. 30, 2013 Integrys Energy Services Natural gas transactions	Jun. 30, 2012 Integrys Energy Services Natural gas transactions	Jun. 30, 2013 Integrys Energy Services Natural gas transactions	Jun. 30, 2012 Integrys Energy Services Natural gas transactions	Apr. 30, 2013 WPS Leasing Integrys Energy Group	Jun. 30, 2012 WPS Leasing Integrys Energy Group	Jun. 30, 2013 WPS Leasing Integrys Energy Group	Jun. 30, 2012 WPS Leasing Integrys Energy Group	Dec. 31, 2012 WPS Leasing Integrys Energy Group
RELATED PARTY TRANSACTIONS
Long-term debt to parent	$ 6.8		$ 7.2																												$ 7.2
Accounts Payable, Related Parties				10.3		10.3		9.2
Liability related to income tax allocation																	7.0	7.4
Amount repaid to related parties	0	22.6	22.6
Sales to related party									0.3	0.2	0.5	0.4							6.0	5.6	11.3	11.0	0.1	0.1	0.2	0.4
Purchases from related party									1.0	1.4	2.0	2.5											0.2	0.2	0.4	0.4
Interest expense																											0.1	0.2	0.3	0.3
Charges from equity method investee for network transmission services				24.6	23.5	49.2	47.1
Charges to equity method investee for services and construction				2.3	2.4	4.1	5.1
Net proceeds from equity method investee's sales of energy to MISO									0	1.0	0	1.8
Income from equity method investee													$ 2.6	$ 2.6	$ 5.1	$ 5.1
Ownership interest (as a percent)													11.53%		11.53%