LONG-TERM DEBT (Details) (USD $) In Millions, unless otherwise specified					1 Months Ended				1 Months Ended				1 Months Ended			1 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 WPS	Dec. 31, 2012 WPS	Feb. 28, 2013 WPS 3.95% Senior Notes due 2013	Mar. 31, 2013 WPS 4.80% Senior Notes due 2013	Mar. 31, 2013 PGL	Dec. 31, 2012 PGL	Apr. 30, 2013 PGL First and Refunding Mortgage Bonds, Series KK, 5.00% bonds due 2033	Apr. 30, 2013 PGL First and Refunding Mortgage Bonds, Series ZZ, 4.00% bonds due 2033	Mar. 31, 2013 PGL First and Refunding Mortgage Bonds, Series NN-2, 4.625% bonds due 2013	Mar. 31, 2013 PGL First and Refunding Mortgage Bonds, Series SS, 7.00% bonds due 2013	Aug. 31, 2013 PGL First and Refunding Mortgage Bonds, Series AAA, 3.96% bonds due 2043 Future funding commitment	Mar. 31, 2013 NSG	Dec. 31, 2012 NSG	May 31, 2013 NSG First Mortgage Series Q, 3.96% bonds due 2043	Mar. 31, 2013 NSG First Mortgage Series N-2, 4.625% bonds due 2013	Mar. 31, 2013 NSG First Mortgage Series O, 7.00% bonds due 2013	Mar. 31, 2013 INTEGRYS ENERGY GROUP, INC.	Dec. 31, 2012 INTEGRYS ENERGY GROUP, INC.
LONG-TERM DEBT
Total	$ 2,224.4	$ 2,246.4	$ 850.1	$ 872.1			$ 625.0	$ 625.0						$ 74.5	$ 74.5				$ 674.8	$ 674.8
Unamortized discount on debt	(1.2)	(1.2)
Total debt	2,223.2	2,245.2
Less current portion	(291.5)	(313.5)				(125.0)					(75.0)	(45.0)					(40.0)	(6.5)
Total long-term debt	1,931.7	1,931.7
Interest rate stated percentage					3.95%	4.80%			5.00%	4.00%	4.625%	7.00%	3.96%			3.96%	4.625%	7.00%
Principal balance repaid					22.0				50.0
Maturity term													30 years
Amount of debt issued										$ 50.0			$ 220.0			$ 54.0