INVESTMENTS IN VARIABLE INTEREST ENTITIES - NARRATIVE (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) entity	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Loss on sale of investments related to dissolution	$ 5.1
Loss on dissolution of variable interest entity	0.0	$ 0.0	$ 4.3
Repayments of investment borrowings related to variable interest entities, amounts due in 2020	2.1
Repayments of investment borrowings related to variable interest entities, amounts due in 2021	27.6
Repayments of investment borrowings related to variable interest entities, amounts due in 2022	99.7
Repayments of investment borrowings related to variable interest entities, amounts due in 2023	340.5
Repayments of investment borrowings related to variable interest entities, amounts due in 2024	314.1
Repayments of investment borrowings related to variable interest entities, amounts due in 2025	183.3
Repayments of investment borrowings related to variable interest entities, amounts due in 2026	120.1
Repayments of investment borrowings related to variable interest entities, amounts due in 2027	63.4
Repayments of investment borrowings related to variable interest entities, amounts due in 2028	0.8
Repayments of investment borrowings related to variable interest entities, amounts due in 2030	7.0
Variable interest entity amortized cost securities held	1,206.3
Variable interest entity, gross unrealized gains fixed maturity securities	3.9
Variable interest entity gross unrealized losses fixed maturity securities	(21.6)
Variable interest entity, estimated fair value of securities held	1,188.6
Variable interest entities net realized loss on investments	(20.5)	(3.6)	(5.6)
Writedowns of investments for other than temporary declines in fair value recognized through net income	3.0		2.5
Variable interest entities net gain (loss) from sale of fixed maturity investments	$ (12.4)		1.2
Number of VIEs in default | entity	1
Investments held by VIEs and sold	$ 280.6	57.2	109.6
Variable interest entity, gross investment losses from sale	12.6	3.8	$ 3.0
Fair value of investments in unrealized loss position for less than 12 months	1,262.8	6,310.7
Gross unrealized losses of investments in unrealized loss position for less than 12 months	11.4	308.6
Fair value of investments in unrealized loss position for more than 12 months	341.2	1,465.0
Gross unrealized losses of investments in unrealized loss position for more than 12 months	9.7	114.7
VIEs
Variable Interest Entity [Line Items]
Loss on dissolution of variable interest entity	5.1
Variable interest entity amortized cost securities held	1.2
Variable Interest Entity
Variable Interest Entity [Line Items]
Fair value of investments in unrealized loss position for less than 12 months	153.0	1,315.7
Gross unrealized losses of investments in unrealized loss position for less than 12 months	3.1	55.7
Fair value of investments in unrealized loss position for more than 12 months	430.1	137.6
Gross unrealized losses of investments in unrealized loss position for more than 12 months	$ 18.5	$ 11.3