GUARANTEES (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014 Integrys Energy Services IES's retail energy business	Sep. 30, 2014 Guarantees supporting commodity transactions	Sep. 30, 2014 Guarantees supporting commodity transactions Integrys Energy Services	Sep. 30, 2014 Guarantees supporting commodity transactions IBS	Sep. 30, 2014 Guarantees supporting commodity transactions MERC	Sep. 30, 2014 Guarantees supporting commodity transactions MGU	Sep. 30, 2014 Guarantees supporting commodity transactions ITF	Sep. 30, 2014 Standby letters of credit	Sep. 30, 2014 Standby letters of credit Integrys Energy Services	Sep. 30, 2014 Standby letters of credit UPPCO	Sep. 30, 2014 Standby letters of credit ITF, MERC, MGU, NSG, PGL, UPPCO, and WPS	Sep. 30, 2014 Surety bonds	Sep. 30, 2014 Other guarantees	Sep. 30, 2014 Other guarantees Integrys Energy Services	Sep. 30, 2014 Other guarantees Integrys Energy Services Texas retail marketing business	Sep. 30, 2014 Other guarantees Integrys Energy Services WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Sep. 30, 2014 Other guarantees ITF	Sep. 30, 2014 Other indemnifications and workers compensation coverage	Nov. 01, 2014 Subsequent Event Other guarantees WPS Power Development
Guarantees
Total guarantees	$ 842.6	$ 586.0	$ 718.3	$ 548.9	$ 5.0	$ 119.0	$ 45.0	$ 0.4	$ 34.6	$ 33.0	$ 0.5	$ 1.6	$ 34.5	$ 55.2	$ 35.0	$ 10.0	$ 1.8	$ 2.4	$ 6.0	$ 41.6
Guarantees expiring in less than 1 year	548.1		478.3						33.8				34.5	1.5
Guarantees expiring within 1 to 3 years	5.3		4.6						0.7				0	0
Guarantees with expiration over 3 years	$ 289.2		$ 235.4						$ 0.1				$ 0	$ 53.7