INVESTMENTS IN VARIABLE INTEREST ENTITIES - NARRATIVE (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) variable_interest_entity	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Variable Interest Entity [Line Items]
Variable interest entity amortized cost securities held	$ 1,518.4
Variable interest entity, gross unrealized gains fixed maturity securities	1.3
Variable interest entity gross unrealized losses fixed maturity securities	31.6
Estimated fair value of fixed maturity securities	1,488.1
Variable interest entities net realized gain (loss) on investments	(4.3)	$ (2.2)
Variable interest entities, write-downs of investments for other than temporary declines in fair value recognized through net income	(3.6)
Variable interest entities, investments sold	47.3	38.7
Variable interest entity, gross investment losses from sale	$ (1.1)	$ 2.4
Number of investments sold at a loss | variable_interest_entity	8
Investments held in limited partnerships	$ 67.0
Unfunded commitments to limited partnerships	64.4
Less than twelve months [Member]
Variable Interest Entity [Line Items]
Fair value investments held by variable interest entity that had been in an unrealized loss position	816.9		$ 1,053.2
Gross unrealized losses in an unrealized loss position for a period	(9.4)		(27.3)
Greater than twelve months [Member]
Variable Interest Entity [Line Items]
Fair value investments held by variable interest entity that had been in an unrealized loss position	339.5		167.4
Gross unrealized losses in an unrealized loss position for a period	(22.2)		$ (4.2)
Continuous Unrealized Position Exceeding 20% of the Amortized Cost Basis for Less Than Six Months [Member]
Variable Interest Entity [Line Items]
Variable interest entity amortized cost securities held	13.0
Estimated fair value of fixed maturity securities	$ 12.3
Minimum [Member]
Variable Interest Entity [Line Items]
Loss as a percent of amortized cost basis for less than six months prior to sale	20.00%
Fixed Income Investments [Member]
Variable Interest Entity [Line Items]
Variable interest entities net realized gain (loss) on investments	$ (0.7)