Regulatory Matters - Utility Rates (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014 Bison Wind Energy Center [Member] MW	Mar. 31, 2014 Bison 4 [Member] MW	Jun. 01, 2011 MPUC 2010 Minnesota Rate Case [Member] Electric Rates [Member] Retail Customers [Member]	Mar. 31, 2014 FERC-Approved Wholesale Rates [Member] Electric Rates [Member] Municipal Customers [Member] Years Customers	Dec. 31, 2012 PSCW 2012 Wisconsin Rate Case [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
Length of Notice Required to Terminate (in Years)				3
Generating Capacity (MW)	292	205
Estimated Capital Expenditures		$ 345
Capital Cost Spent to Date		$ 187.1