FAIR VALUE - FINANCIAL INSTRUMENTS NOT RECORDED AT FAIR VALUE (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying value and estimated fair value of financial instruments
Long-term debt to parent	$ 5.7	$ 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	5.7	6.3
Preferred stock	51.2	51.2
Fair Value
Carrying value and estimated fair value of financial instruments
Long-term debt	1,250.1	1,176.5
Long-term debt to parent	6.0	7.1
Preferred stock	$ 57.1	$ 61.4