PREFERRED STOCK OF SUBSIDIARY (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Preferred stock of subsidiary
Authorized shares	1,000,000
Par value (in dollars per share)	$ 100
Shares outstanding	510,495
Carrying value	$ 51.1	$ 51.1
WPS
Preferred stock of subsidiary
Authorized shares	1,000,000
Mandatorily redeemable shares	0
Par value (in dollars per share)	$ 100
Shares outstanding	510,495	510,495
Carrying value	51.1	51.1
Notice period for redemption of preferred stock	30 days
Pre-emptive, subscription, or conversion rights	0
Sinking fund provisions	0
WPS | 5.00% Preferred Stock Series
Preferred stock of subsidiary
Series (as a percent)	5.00%
Shares outstanding	130,692	130,692
Carrying value	13.1	13.1
WPS | 5.04% Preferred Stock Series
Preferred stock of subsidiary
Series (as a percent)	5.04%
Shares outstanding	29,898	29,898
Carrying value	3.0	3.0
WPS | 5.08% Preferred Stock Series
Preferred stock of subsidiary
Series (as a percent)	5.08%
Shares outstanding	49,905	49,905
Carrying value	5.0	5.0
WPS | 6.76% Preferred Stock Series
Preferred stock of subsidiary
Series (as a percent)	6.76%
Shares outstanding	150,000	150,000
Carrying value	15.0	15.0
WPS | 6.88% Preferred Stock Series
Preferred stock of subsidiary
Series (as a percent)	6.88%
Shares outstanding	150,000	150,000
Carrying value	$ 15.0	$ 15.0