Regulatory Matters - Electric Rates (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Bison Wind Energy Center [Member] MW	Jun. 01, 2011 MPUC 2010 Minnesota Rate Case [Member] Electric Rates [Member] Retail Customers [Member]	Mar. 31, 2013 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Municipal Customers [Member] Years Customers	Mar. 31, 2013 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Non-Affiliated Private Utility [Member] Years Customers	Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Retail Customers [Member]	Dec. 31, 2012 PSCW 2012 Wisconsin Rate Case [Member] Retail Customers [Member]	Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Electric Rates [Member] Retail Customers [Member]	Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Natural Gas Rates [Member] Retail Customers [Member]	Mar. 31, 2013 PSCW 2012 Wisconsin Rate Case [Member] Water Rates [Member] Retail Customers [Member]
Rate Regulation [Line Items]
Approved Rate of Return on Common Equity		10.38%				10.90%
Approved Percentage of Capital Structure Related to Equity		54.29%
Number of Customers			16	1
Length of Notice Required to Terminate (in Years)			3	2
Approved Rate Increase or Decrease					2.40%		1.20%	(0.20%)	13.80%
Amount Of Estimated Additional Revenue					$ 1.7
Generating Capacity (MW)	292