SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES PROPERTY, PLANT, AND EQUIPMENT (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended									3 Months Ended	12 Months Ended
	Dec. 31, 2013 Software Minimum	Dec. 31, 2013 Software Maximum	Dec. 31, 2013 MERC	Dec. 31, 2012 MERC	Dec. 31, 2011 MERC	Dec. 31, 2013 MERC Minnesota Public Utilities Commission (MPUC)	Dec. 31, 2013 MGU	Dec. 31, 2012 MGU	Dec. 31, 2011 MGU	Mar. 31, 2013 MGU Michigan Public Service Commission (MPSC)	Dec. 31, 2013 NSG	Dec. 31, 2012 NSG	Dec. 31, 2011 NSG	Dec. 31, 2013 PGL	Dec. 31, 2012 PGL	Dec. 31, 2011 PGL	Dec. 31, 2013 UPPCO	Dec. 31, 2012 UPPCO	Dec. 31, 2011 UPPCO	Dec. 31, 2013 WPS Electric	Dec. 31, 2012 WPS Electric	Dec. 31, 2011 WPS Electric	Dec. 31, 2013 WPS Natural gas	Dec. 31, 2012 WPS Natural gas	Dec. 31, 2011 WPS Natural gas
Property, plant, and equipment
Annual utility composite depreciation rate (as a percent)			1.88%	3.07%	3.10%		1.93%	2.71%	2.73%		2.44%	2.43%	2.42%	3.19%	3.16%	3.18%	3.29%	3.31%	3.33%	2.79%	2.87%	2.88%	2.19%	2.21%	2.22%
Useful life	3 years	15 years
Reduction to depreciation expense						$ 2.0				$ 2.5