SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS FAIR VALUE OF FINANCIAL INSTRUMENTS - RELATED PARTIES (Details) (Integrys Energy Group, Inc., USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Financial instruments not recorded at fair value
Long-term notes receivable from related parties	$ 224.3	$ 171.2
Current portion of long-term notes receivable from related parties	10.0	72.0
Carrying Amount
Financial instruments not recorded at fair value
Long-term notes receivable from related parties	224.3	171.2
Current portion of long-term notes receivable from related parties	10.0	72.0
Fair value
Financial instruments not recorded at fair value
Long-term notes receivable from related parties	238.5	202.1
Current portion of long-term notes receivable from related parties	$ 10.2	$ 73.4