REGULATORY ENVIRONMENT (Details) (Public Service Commission of Wisconsin (PSCW), USD $) In Millions, unless otherwise specified				12 Months Ended
	Mar. 29, 2013 2014 Rates Entity's Original Request	Mar. 29, 2013 2014 Rates Retail electric rate case Entity's Original Request	Mar. 29, 2013 2014 Rates Natural gas rate case Entity's Original Request	Dec. 31, 2012 2013 Rates Settlement agreement	Dec. 06, 2012 2013 Rates Settlement agreement	Mar. 31, 2013 2013 Rates Retail electric rate case Settlement agreement	Dec. 06, 2012 2013 Rates Retail electric rate case Settlement agreement	Dec. 06, 2012 2013 Rates Natural gas rate case Settlement agreement	Dec. 09, 2011 2012 Rates Retail electric rate case Rate Order	Dec. 09, 2011 2012 Rates Natural gas rate case Rate Order
Regulatory Proceedings:
Rate increase (decrease)						$ 0	$ 28.5	$ (3.4)	$ 8.1	$ (7.2)
Rate Increase (decrease)		71.1	19.0
Estimated fuel refund							20.5
Deferred regulatory liability related to employee benefits								2.4
Percent return on equity					10.30%
Percent return on equity	10.75%
Equity ratio percent					51.61%
Equity ratio percent	51.11%
Annual cap on rates							14.0	8.0
Authorized recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act				$ 5.9
Percentage of price variance from the cost of fuel and purchased power included in rates									2.00%