RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended		3 Months Ended			3 Months Ended						3 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2013 ATC	Mar. 31, 2012 ATC	Dec. 31, 2012 ATC	Mar. 31, 2013 WRPC	Mar. 31, 2012 WRPC	Mar. 31, 2013 WPS Investments, LLC	Mar. 31, 2012 WPS Investments, LLC	Mar. 31, 2013 Integrys Energy Group	Dec. 31, 2012 Integrys Energy Group	Mar. 31, 2013 UPPCO Electric transactions	Mar. 31, 2012 UPPCO Electric transactions	Mar. 31, 2013 Integrys Energy Services Natural gas transactions	Mar. 31, 2012 Integrys Energy Services Natural gas transactions	Mar. 31, 2013 WPS Leasing Integrys Energy Group	Mar. 31, 2012 WPS Leasing Integrys Energy Group	Dec. 31, 2012 WPS Leasing Integrys Energy Group
RELATED PARTY TRANSACTIONS
Notes payable		$ 7.2	$ 7.0														$ 7.0		$ 7.2
Accounts Payable				10.3		9.2
Liability related to income tax allocation											7.2	7.4
Amount repaid to related parties	22.6	22.6
Net proceeds from equity method investee's sales of energy to MISO								0.8
Sales to related party							0.2	0.2					5.3	5.3	0.1	0.3
Purchases from related party							1.0	1.2							0.2	0.2
Interest expense																	0.2	0.2
Charges from equity method investee for network transmission services				24.6	23.5
Charges to equity method investee for services and construction				1.8	2.6
Equity earnings from equity method investee									$ 2.5	$ 2.5
Ownership interest (as a percent)									11.66%