RISK MANAGEMENT ACTIVITIES - INTEGRYS ENERGY SERVICES SEGMENT, NOTIONAL VOLUMES (Details) (Non-hedge derivatives, Integrys Energy Services)	9 Months Ended	12 Months Ended
	Sep. 30, 2014 MMBTU	Dec. 31, 2013 MMBTU
Natural gas contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	143,230,000	119,990,000
Natural gas contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	118,250,000	106,540,000
Electric contracts | Purchases
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	40,987,700,000	49,186,300,000
Electric contracts | Sales
Risk management activities
Notional volume of outstanding derivative contracts (mmbtu or kwh)	23,657,900,000	30,813,800,000