FAIR VALUE - FINANCIAL INSTRUMENTS NOT RECORDED AT AT FAIR VALUE (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Carrying value and estimated fair value of financial instruments
Long-term debt to parent	$ 6.1	$ 6.3
Preferred stock	51.2	51.2
Carrying Amount
Carrying value and estimated fair value of financial instruments
Long-term debt	1,174.5	1,174.5
Long-term debt to parent	6.1	6.3
Preferred stock	51.2	51.2
Fair Value
Carrying value and estimated fair value of financial instruments
Long-term debt	1,199.6	1,176.5
Long-term debt to parent	6.7	7.1
Preferred stock	$ 57.4	$ 61.4