INVESTMENTS IN VARIABLE INTEREST ENTITIES - NARRATIVE (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) investment	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) investment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Total amortized cost	$ 1,223.7		$ 1,223.7
Variable interest entity, gross unrealized gains fixed maturity securities	1.8		1.8
Variable interest entity gross unrealized losses fixed maturity securities	30.7		30.7
Variable interest entity, allowance for credit losses fixed maturity securities	22.2		22.2
Estimated fair value of fixed maturity securities	1,172.6		1,172.6
Variable interest entities net realized losses on investments			17.9	$ 15.8
Variable interest entities net loss from sale of fixed maturity investments			5.6	10.7
Variable interest entities, change in allowance for credit losses	5.6		(12.3)
Variable interest entity, gross investment losses from sale			5.7	10.9
Variable interest entities, investments sold			47.3	276.8
Loss on dissolution of variable interest entity	$ 0.0	$ 0.0	$ 0.0	5.1
Number of investments held by VIE, in default | investment	6		6
Fair value, less than 12 months	$ 1,573.0		$ 1,573.0		$ 1,262.8
Gross unrealized losses, less than 12 months	54.9		54.9		11.4
Fair value, 12 months or greater	294.7		294.7		341.2
Gross unrealized losses, 12 months or greater	8.5		8.5		9.7
Investments held in limited partnerships	557.1		557.1
Unfunded commitments to limited partnerships	78.8		78.8
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total amortized cost	11.4		11.4
Variable interest entity, allowance for credit losses fixed maturity securities	5.0		5.0
Loss on dissolution of variable interest entity				$ 5.1
Variable interest entity carrying value	6.2		6.2
Fair value, less than 12 months	643.0		643.0		153.0
Gross unrealized losses, less than 12 months	14.3		14.3		3.1
Fair value, 12 months or greater	196.4		196.4		430.1
Gross unrealized losses, 12 months or greater	$ 7.4		$ 7.4		$ 18.5