ACQUISITIONS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						1 Months Ended			1 Months Ended	0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 WPS Senior Notes, 4.752% due 2044	Nov. 30, 2013 WPS Senior Notes, 4.752% due 2044	Dec. 31, 2013 Alliant Energy Corporation's Natural Gas Distribution Business in Southeast Minnesota MERC	May 31, 2013 Compass Energy Services Inc Integrys Energy Services	May 31, 2013 Compass Energy Services Inc Integrys Energy Services Minimum	May 31, 2013 Compass Energy Services Inc Integrys Energy Services Maximum	Mar. 31, 2013 Fox Energy Company LLC WPS MW	Sep. 02, 2011 Trillium USA and Pinnacle CNG Systems Integrys Energy Group, Inc. business	Dec. 31, 2012 Trillium USA and Pinnacle CNG Systems Integrys Energy Group, Inc.
Acquisitions
Estimated purchase price						$ 11
Amount paid for the acquisition							12.4			391.6
Contingent Consideration								3.0	8.0
Period of financial performance of acquiree as basis for contingent consideration							5 years
Liabilities recorded related to contingent consideration							7.8
Assets acquired
Inventories							0.7			3.0
Assets from risk management 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
Capacity of Fox Energy Center (in megawatts)										593
Contracted capacity under tolling arrangement (in megawatts)										500
Contract termination fee related to tolling arrangement	(50.0)	0	0							50.0
Amortization period of regulatory asset										9 years
Interest rate stated percentage				4.752%	4.752%
Number of businesses acquired											2
Total consideration paid											49.6
Total cash paid net of cash acquired	391.6	0	0								42.6
Cash acquired											$ 7.0	$ 1.3