ACQUISITIONS (Details) (USD $) In Millions, unless otherwise specified		1 Months Ended
	Sep. 30, 2013 Alliant Energy Corporation's Natural Gas Distribution Business in Southeast Minnesota [Member] MERC	May 31, 2013 Compass Energy Services Inc [Member] Subsidiary Integrys Energy Services [Member]	May 31, 2013 Compass Energy Services Inc [Member] Subsidiary Integrys Energy Services [Member] Minimum	May 31, 2013 Compass Energy Services Inc [Member] Subsidiary Integrys Energy Services [Member] Maximum	Mar. 31, 2013 Fox Energy Company LLC WPS MW
Acquisitions
Period of financial performance of acquiree as basis for contingent consideration		5 years
Liabilities recorded related to contingent consideration		$ 7.7
Contingent Consideration			3.0	8.0
Capacity of Fox Energy Center (in megawatts)					593
Contracted capacity under tolling arrangement (in megawatts)					500
Amount paid for the acquisition	11.0	12.4			391.6
Contract termination fee related to tolling arrangement					50.0
Amortization period of regulatory asset					9 years
Assets acquired
Inventories		0.7			3.0
Assets from risk managment activities (current)		15.1
Other current assets		1.1			0.4
Assets from risk management activities (long-term)		9.3
Property, plant, and equipment					374.4
Other long-term assets		6.1			15.6
Total assets acquired		32.3			393.4
Liabilities assumed
Accounts payable					1.8
Liabilities from risk management activities (current)		8.3
Other current liabilities		0.5
Liabilities from risk management activities (long-term)		3.4
Total liabilities assumed		$ 12.2			$ 1.8