FAIR VALUE MEASUREMENTS - FAIR VALUE ACTIVITY (Details) - Significant unobservable inputs (Level 3) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Corporate securities
Assets:
Purchases	$ 11.3	$ 1.7	$ 14.2	$ 2.7
Sales	(5.1)	0.0	(3.6)	(1.4)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	6.2	1.7	10.6	1.3
Asset-backed securities
Assets:
Purchases	0.0	0.3	0.0	2.5
Sales	(0.2)	(0.2)	(0.3)	(7.5)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	(0.2)	0.1	(0.3)	(5.0)
Total Fixed Maturities, Available For Sale
Assets:
Purchases	11.3	2.0	14.2	5.2
Sales	(5.3)	(0.2)	(3.9)	(8.9)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	6.0	1.8	10.3	(3.7)
Equity securities - corporate securities
Assets:
Purchases		0.0		0.0
Sales		(2.1)		(2.1)
Issuances		0.0		0.0
Settlements		0.0		0.0
Purchases, sales, issuances and settlements, net	0.0	(2.1)	0.0	(2.1)
Trading securities - commercial mortgage-backed securities
Assets:
Purchases, sales, issuances and settlements, net	0.0		0.0
Other invested assets - residual tranches
Assets:
Purchases	8.6	0.1	19.4	1.8
Sales	(3.0)	0.0	(4.4)	(0.3)
Issuances	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Purchases, sales, issuances and settlements, net	$ 5.6	0.1	$ 15.0	1.5
Non-agency residential mortgage-backed securities
Assets:
Purchases, sales, issuances and settlements, net		0.0		0.0
Collateralized loan obligations
Assets:
Purchases, sales, issuances and settlements, net				0.0
Trading securities - non-agency residential mortgage-backed securities
Assets:
Purchases, sales, issuances and settlements, net		$ 0.0		$ 0.0

Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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