Segment Information - Pre-tax income (loss) from exited business (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pre-tax income (loss) from exited business:
Change in fair value of funds withheld embedded derivative	$ (1,085.7)	$ 3,652.8	$ 0.0
Net realized capital gains on funds withheld assets	165.0	749.4
Amortization of reinsurance loss	(17.7)	(19.3)	$ (23.0)
Total pre-tax income (loss) from exited business	(1,129.8)	4,260.1
Operating Segments
Pre-tax income (loss) from exited business:
Change in fair value of funds withheld embedded derivative	(1,085.7)	3,652.8
Net realized capital gains on funds withheld assets	165.0	749.4
Strategic review costs and impacts on pre-tax income (loss)		40.4
Amortization of reinsurance loss	(68.7)	(56.7)
Other impacts of reinsured business	(140.4)	(125.8)
Total pre-tax income (loss) from exited business	$ (1,129.8)	$ 4,260.1