INVESTMENTS - SCHEDULE OF INVESTMENTS WITH UNREALIZED LOSSES CLASSIFIED BY CONTRACTUAL MATURITY DATE (Details) $ in Millions	Dec. 31, 2022 USD ($)
Amortized cost
Due in one year or less	$ 91.2
Due after one year through five years	1,741.9
Due after five years through ten years	1,845.3
Due after ten years	11,631.2
Subtotal	15,309.6
Structured securities	6,040.1
Total	21,349.7
Estimated fair value
Due in one year or less	89.8
Due after one year through five years	1,615.5
Due after five years through ten years	1,649.8
Due after ten years	9,485.8
Subtotal	12,840.9
Structured securities	5,385.9
Total	$ 18,226.8