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															1 Months Ended			1 Months Ended			1 Months Ended			1 Months Ended					1 Months Ended															1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Maximum	Dec. 31, 2013 WPS Maximum	Dec. 31, 2013 WPS First Mortgage	Dec. 31, 2012 WPS First Mortgage	Dec. 31, 2013 WPS Senior Notes, 4.80% due 2013	Dec. 31, 2012 WPS Senior Notes, 4.80% due 2013	Feb. 28, 2013 WPS Senior Notes, 3.95% due 2013	Dec. 31, 2013 WPS Senior Notes, 3.95% due 2013	Dec. 31, 2012 WPS Senior Notes, 3.95% due 2013	Dec. 31, 2013 WPS Senior Notes, 6.375% due 2015	Dec. 31, 2012 WPS Senior Notes, 6.375% due 2015	Dec. 31, 2013 WPS Senior Notes, 5.65% due 2017	Dec. 31, 2012 WPS Senior Notes, 5.65% due 2017	Dec. 31, 2013 WPS Senior Notes, 6.08% due 2028	Dec. 31, 2012 WPS Senior Notes, 6.08% due 2028	Dec. 31, 2013 WPS Senior Notes, 5.55% due 2036	Dec. 31, 2012 WPS Senior Notes, 5.55% due 2036	Dec. 31, 2013 WPS Senior Notes, 3.671% due 2042	Dec. 31, 2012 WPS Senior Notes, 3.671% due 2042	Nov. 30, 2013 WPS Senior Notes, 4.752% due 2044	Dec. 31, 2013 WPS Senior Notes, 4.752% due 2044	Dec. 31, 2012 WPS Senior Notes, 4.752% due 2044	Dec. 31, 2013 PGL Maximum	Apr. 30, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series KK, 5.00% bonds due 2033	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series KK, 5.00% bonds due 2033	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series KK, 5.00% bonds due 2033	May 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series NN-2, 4.625% bonds due 2013	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series NN-2, 4.625% bonds due 2013	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series NN-2, 4.625% bonds due 2013	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series QQ, 4.875% bonds due 2038	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series QQ, 4.875% bonds due 2038	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series RR, 4.30% bonds due 2035	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series RR, 4.30% bonds due 2035	Nov. 30, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series SS, 7.00% bonds due 2013	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series SS, 7.00% bonds due 2013	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series SS, 7.00% bonds due 2013	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series TT, 8.00% bonds due 2018	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series TT, 8.00% bonds due 2018	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series UU, 4.63% bonds due 2019	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series UU, 4.63% bonds due 2019	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series VV, 2.125% bonds due 2030	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series VV, 2.125% bonds due 2030	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series WW, 2.625% bonds due 2033	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series WW, 2.625% bonds due 2033	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series XX, 2.21% bonds due 2016	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series XX, 2.21% bonds due 2016	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series YY, 3.98% bonds due 2042	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series YY, 3.98% bonds due 2042	Apr. 30, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series ZZ, 4.0% bonds due 2033	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series ZZ, 4.0% bonds due 2033	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series ZZ, 4.0% bonds due 2033	Aug. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series AAA, 3.96% bonds due 2043	Dec. 31, 2013 PGL Fixed First and Refunding Mortgage Bonds, Series AAA, 3.96% bonds due 2043	Dec. 31, 2012 PGL Fixed First and Refunding Mortgage Bonds, Series AAA, 3.96% bonds due 2043	May 31, 2013 NSG First Mortgage Series N-2, 4.625% bonds due 2013	Dec. 31, 2013 NSG First Mortgage Series N-2, 4.625% bonds due 2013	Dec. 31, 2012 NSG First Mortgage Series N-2, 4.625% bonds due 2013	Nov. 30, 2013 NSG First Mortgage Series O, 7.00% bonds due 2013	Dec. 31, 2013 NSG First Mortgage Series O, 7.00% bonds due 2013	Dec. 31, 2012 NSG First Mortgage Series O, 7.00% bonds due 2013	Dec. 31, 2013 NSG First Mortgage Series P, 3.43% bonds due 2027	Dec. 31, 2012 NSG First Mortgage Series P, 3.43% bonds due 2027	May 31, 2013 NSG First Mortgage Series Q, 3.96% bonds due 2043	Dec. 31, 2013 NSG First Mortgage Series Q, 3.96% bonds due 2043	Dec. 31, 2012 NSG First Mortgage Series Q, 3.96% bonds due 2043	Dec. 31, 2013 Integrys Energy Group, Inc.	Dec. 31, 2012 Integrys Energy Group, Inc.	Dec. 31, 2013 Integrys Energy Group, Inc. Maximum	Dec. 31, 2013 Integrys Energy Group, Inc. Unsecured Senior Notes, 7.27% due 2014	Dec. 31, 2012 Integrys Energy Group, Inc. Unsecured Senior Notes, 7.27% due 2014	Dec. 31, 2013 Integrys Energy Group, Inc. Unsecured Senior Notes, 8.00% due 2016	Dec. 31, 2012 Integrys Energy Group, Inc. Unsecured Senior Notes, 8.00% due 2016	Dec. 31, 2013 Integrys Energy Group, Inc. Unsecured Senior Notes, 4.17% due 2020	Dec. 31, 2012 Integrys Energy Group, Inc. Unsecured Senior Notes, 4.17% due 2020	Dec. 31, 2013 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.11% due 2066	Dec. 31, 2012 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.11% due 2066	Dec. 31, 2013 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.11% due 2066 Maximum	Aug. 31, 2013 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.00% due 2073	Dec. 31, 2013 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.00% due 2073	Dec. 31, 2012 Integrys Energy Group, Inc. Junior Subordinated Notes, 6.00% due 2073
LONG-TERM DEBT
Interest rate stated percentage					7.125%		4.80%		3.95%	3.95%		6.375%		5.65%		6.08%		5.55%		3.671%		4.752%	4.752%			5.00%	5.00%		4.625%	4.625%		4.875%		4.30%		7.00%	7.00%		8.00%		4.63%		2.125%		2.625%		2.21%		3.98%		4.00%	4.00%		3.96%	3.96%		4.625%	4.625%		7.00%	7.00%		3.43%		3.96%	3.96%					7.27%		8.00%		4.17%		6.11%			6.00%	6.00%
Total	$ 3,056.9	$ 2,246.4			$ 0.1	$ 0.1	$ 0	$ 125.0		$ 0	$ 22.0	$ 125.0	$ 125.0	$ 125.0	$ 125.0	$ 50.0	$ 50.0	$ 125.0	$ 125.0	$ 300.0	$ 300.0		$ 450.0	$ 0			$ 0	$ 50.0		$ 0	$ 75.0	$ 75.0	$ 75.0	$ 50.0	$ 50.0		$ 0	$ 45.0	$ 5.0	$ 5.0	$ 75.0	$ 75.0	$ 50.0	$ 50.0	$ 50.0	$ 50.0	$ 50.0	$ 50.0	$ 100.0	$ 100.0		$ 50.0	$ 0		$ 220.0	$ 0		$ 0	$ 40.0		$ 0	$ 6.5	$ 28.0	$ 28.0		$ 54.0	$ 0				$ 100.0	$ 100.0	$ 55.0	$ 55.0	$ 250.0	$ 250.0	$ 269.8	$ 269.8			$ 400.0	$ 0
Unamortized discount on debt	(0.7)	(1.2)
Total debt	3,056.2	2,245.2
Less current portion	100.0	313.5																																																																		100.0	0		100.0
Total long-term debt	2,956.2	1,931.7																																																																		974.7	674.7
Principal balance repaid							125.0		22.0																	50.0			75.0							45.0																					40.0			6.5
Amount of debt issued																						$ 450.0																													$ 50.0			$ 220.0											$ 54.0															$ 400.0
Maximum percentage of notes that can be redeemed or repurchased without replacement																																																																															10.00%
Debt to capitalization ratio required to be maintained (as a percent)			65.00%	65.00%																					65.00%																																													65.00%