SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 7)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
WPS | Electric
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	2.88%	3.05%	3.04%
WPS | Natural gas
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	2.22%	3.28%	3.30%
UPPCO
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	3.33%	3.18%	3.05%
MGU
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	2.73%	3.55%	2.66%
MERC
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	3.10%	3.08%	3.10%
PGL
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	3.18%	3.10%	2.29%
NSG
Property, plant, and equipment
Annual Utility Composite Depreciation Rates (as a percent)	2.42%	2.35%	1.66%
Software
Property, plant, and equipment
Useful life, low end of range (in years)	3
Useful life, high end of range (in years)	15