FAIR VALUE - FINANCIAL INSTRUMENTS NOT RECORDED AT FAIR VALUE (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Carrying value and estimated fair value of financial instruments
Long-term Debt	$ 3,081.3	$ 3,081.3
Preferred stock	51.1	51.1
Carrying Amount
Carrying value and estimated fair value of financial instruments
Long-term Debt	3,081.3	3,081.3
Preferred stock	51.1	51.1
Fair value
Carrying value and estimated fair value of financial instruments
Long-term Debt	3,112.9	3,271.4
Preferred stock	$ 53.1	$ 51.8