LONG-TERM DEBT (Details) (USD $) In Millions, unless otherwise specified						1 Months Ended			1 Months Ended			1 Months Ended			1 Months Ended		1 Months Ended				1 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 WPS	Dec. 31, 2012 WPS	Jun. 30, 2013 WPS WPS Senior Notes, 4.80% due 2013	Feb. 28, 2013 WPS WPS Senior Notes, 3.95% due 2013	Jun. 30, 2013 PGL	Dec. 31, 2012 PGL	Apr. 30, 2013 PGL PGL Fixed First and Refunding Mortgage Bonds, Series KK, 5.00% bonds due 2033	May 31, 2013 PGL PGL Fixed First and Refunding Mortgage Bonds, Series NN-2, 4.625% bonds due 2013	Jun. 30, 2013 PGL PGL Fixed First and Refunding Mortgage Bonds, Series SS, 7.00% bonds due 2013	Apr. 30, 2013 PGL PGL Fixed First and Refunding Mortgage Bonds, Series ZZ, 4.0% bonds due 2033	Jun. 30, 2013 NSG	Dec. 31, 2012 NSG	May 31, 2013 NSG NSG First Mortgage Series N-2, 4.625% bonds due 2013	Jun. 30, 2013 NSG NSG First Mortgage Series O, 7.00% bonds due 2013	May 31, 2013 NSG NSG First Mortgage Series Q, 3.96% bonds due 2043	Jun. 30, 2013 Integrys Energy Group, Inc.	Dec. 31, 2012 Integrys Energy Group, Inc.	Jun. 30, 2013 Integrys Energy Group, Inc. TEG Unsecured Senior Notes, 7.27% due 2014	Aug. 31, 2013 Subsequent Event PGL PGL Fixed First and Refunding Mortgage Bonds, Series AAA, 3.96% bonds due 2043
LONG-TERM DEBT
Total	$ 2,163.4	$ 2,246.4	$ 850.1	$ 872.1			$ 550.0	$ 625.0					$ 88.5	$ 74.5				$ 674.8	$ 674.8
Unamortized discount on debt	(0.7)	(1.2)
Total debt	2,162.7	2,245.2
Less current portion	(276.5)	(313.5)			(125.0)						(45.0)					(6.5)				(100.0)
Total long-term debt	1,886.2	1,931.7
Interest rate stated percentage					4.80%	3.95%			5.00%	4.625%	7.00%	4.00%			4.625%	7.00%	3.96%			7.27%	3.96%
Principal balance repaid						22.0			50.0	75.0					40.0
Maturity term																					30 years
Amount of debt issued												50.0					54.0				220.0
Less long-term debt held for sale	$ 0	$ (0.2)