LONG-TERM DEBT (Details) (USD $) In Millions, unless otherwise specified														1 Months Ended		0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 WPS	Dec. 31, 2013 WPS	Sep. 30, 2014 PGL	Dec. 31, 2013 PGL	Sep. 30, 2014 NSG	Dec. 31, 2013 NSG	Sep. 30, 2014 Integrys Energy Group, Inc.	Dec. 31, 2013 Integrys Energy Group, Inc.	Sep. 30, 2014 Fixed First and Refunding Mortgage VV Series 2.125 Percent Bonds, Due 2030 PGL	Jun. 30, 2014 Fixed First and Refunding Mortgage VV Series 2.125 Percent Bonds, Due 2030 PGL	Sep. 30, 2014 Fixed First and Refunding Mortgage VV Series 3.9 Percent Bonds, Due 2030 PGL	Jun. 30, 2014 Unsecured Senior Notes 7.27 Percent, Due 2014 Integrys Energy Group, Inc.	Jun. 01, 2014 Unsecured Senior Notes 7.27 Percent, Due 2014 Integrys Energy Group, Inc.	Nov. 03, 2014 Subsequent Event Fixed First and Refunding Mortgage BBB Series 4.21 Percent Bonds, Due 2044 PGL	Nov. 03, 2014 Subsequent Event Fixed First and Refunding Mortgage QQ Series 4.875 Percent Bonds, Due 2038 PGL
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,956.9	$ 3,056.9	$ 1,175.1	$ 1,175.1	$ 725.0	$ 725.0	$ 82.0	$ 82.0	$ 974.8	$ 1,074.8	$ 50.0
Unamortized discount on debt	(0.6)	(0.7)
Total debt	2,956.3	3,056.2
Current portion of long-term debt	0	100.0
Long-term debt	2,956.3	2,956.2
Debt Instrument, Interest Rate, Stated Percentage												2.13%	3.90%		7.27%	4.21%	4.88%
Repayments of Debt														100.0			75.0
Proceeds from debt issuance																$ 200.0