SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS SHORT-TERM NOTES PAYABLE - RELATED PARTIES (Details) (Integrys Energy Group, Inc., USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
SHORT-TERM NOTES PAYABLE - RELATED PARTIES
Short-term notes payable to related parties	$ 126.2	$ 165.7
PELLC
SHORT-TERM NOTES PAYABLE - RELATED PARTIES
Short-term notes payable to related parties	43.5	165.7
ITF
SHORT-TERM NOTES PAYABLE - RELATED PARTIES
Short-term notes payable to related parties	8.6	0
PDI
SHORT-TERM NOTES PAYABLE - RELATED PARTIES
Short-term notes payable to related parties	$ 74.1	$ 0