SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS LONG-TERM NOTES RECEIVABLE - RELATED PARTIES (Details) (Integrys Energy Group, Inc., USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Total notes receivable from related parties	$ 183.4	$ 234.3
Less current portion	2.5	10.0
Long-term notes receivable from related parties	180.9	224.3
WPS Leasing | Notes Receivable 8.76 Percent Due 2015
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	8.76%
Total notes receivable from related parties	2.0	2.4
WPS Leasing | Notes Receivable 7.35 Percent Due 2016
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	7.35%
Total notes receivable from related parties	3.4	3.9
UPPCO | Notes Receivable 6.059 Percent Due 2017
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	6.059%
Total notes receivable from related parties	0	15.0
UPPCO | Notes Receivable 3.35 Percent Due 2018
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	3.35%
Total notes receivable from related parties	0	10.0
UPPCO | Notes Receivable 5.041 Percent Due 2020
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	5.041%
Total notes receivable from related parties	0	15.0
UPPCO | Notes Receivable 3.99 Percent Due 2023
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	3.99%
Total notes receivable from related parties	0	20.0
MERC | Notes Receivable 3.99 Percent Due 2023
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	3.99%
Total notes receivable from related parties	29.0	29.0
MERC | Notes Receivable 6.16 Percent Due 2016
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	6.16%
Total notes receivable from related parties	29.0	29.0
MERC | Notes Receivable 6.40 Percent Due 2021
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	6.40%
Total notes receivable from related parties	29.0	29.0
MERC | Notes Receivable 3.57 Percent Due 2024
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	3.57%
Total notes receivable from related parties	20.0	0
MGU | Notes Receivable 5.76 Percent Due 2016
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	5.76%
Total notes receivable from related parties	28.0	28.0
MGU | Notes Receivable 5.98 Percent Due 2021
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	5.98%
Total notes receivable from related parties	28.0	28.0
MGU | Notes Receivable 3.00 Percent Due 2023
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	3.00%
Total notes receivable from related parties	15.0	15.0
IBS | Notes Receivable 6.865 Percent Due 2014
LONG-TERM NOTES RECEIVABLE - RELATED PARTIES
Interest rate stated percentage	6.865%
Total notes receivable from related parties	$ 0	$ 10.0