GUARANTEES (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Guarantees
Total guarantees	$ 843.0
Guarantees expiring in less than 1 year	513.9
Guarantees expiring within 1 to 3 years	35.0
Guarantees with expiration over 3 years	294.1
Integrys Energy Services | Texas Retail Electric Marketing Business
Guarantees
Total guarantees	10.0
Integrys Energy Services | Sale of Stoneman generation facility
Guarantees
Total guarantees	1.8
UPPCO
Guarantees
Total guarantees	3.4
Guarantees supporting commodity transactions
Guarantees
Total guarantees	684.5
Guarantees expiring in less than 1 year	412.6
Guarantees expiring within 1 to 3 years	31.7
Guarantees with expiration over 3 years	240.2
Guarantees supporting commodity transactions | Integrys Energy Services
Guarantees
Total guarantees	497.7
Guarantees supporting commodity transactions | ITF
Guarantees
Total guarantees	0.2
Guarantees supporting commodity transactions | MERC
Guarantees
Total guarantees	126.7
Guarantees supporting commodity transactions | IBS
Guarantees
Total guarantees	5.0
Guarantees supporting commodity transactions | MGU
Guarantees
Total guarantees	52.9
Guarantees supporting commodity transactions | UPPCO
Guarantees
Total guarantees	2.0
Standby letters of credit
Guarantees
Total guarantees	74.1
Guarantees expiring in less than 1 year	70.7
Guarantees expiring within 1 to 3 years	3.3
Guarantees with expiration over 3 years	0.1
Standby letters of credit | Integrys Energy Services
Guarantees
Total guarantees	72.1
Standby letters of credit | ITF, MERC, MGU, NSG, PGL, UPPCO, and WPS
Guarantees
Total guarantees	2.0
Surety bonds
Guarantees
Total guarantees	29.1
Guarantees expiring in less than 1 year	29.1
Guarantees expiring within 1 to 3 years	0
Guarantees with expiration over 3 years	0
Other guarantees
Guarantees
Total guarantees	55.3
Guarantees expiring in less than 1 year	1.5
Guarantees expiring within 1 to 3 years	0
Guarantees with expiration over 3 years	53.8
Other guarantees | Integrys Energy Services
Guarantees
Total guarantees	35.0
Other guarantees | ITF
Guarantees
Total guarantees	2.4
Indemnification and workers' compensation coverage
Guarantees
Total guarantees	$ 6.1