Segment Information - Pre-tax income (loss) from exited business (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pre-tax income (loss) from exited business:
Change in fair value of funds withheld embedded derivative		$ 925.6	$ 1,237.7	$ 392.9	$ 4,305.0
Net realized capital gains (losses) on funds withheld assets	[1]	1.0	8.5	119.8	697.5
Total pre-tax income (loss) from exited business		879.2	1,178.9	352.3	4,903.4
Reconciling Items
Pre-tax income (loss) from exited business:
Change in fair value of funds withheld embedded derivative		925.6	1,237.7	392.9	4,305.0
Net realized capital gains (losses) on funds withheld assets		1.0	8.5	119.8	697.5
Strategic review costs and impacts on pre-tax income (loss)			(27.6)		36.4
Amortization of reinsurance gain (loss)		(8.1)	(7.7)	(50.5)	(38.2)
Other impacts of reinsured business		(39.3)	(32.0)	(109.9)	(97.3)
Total pre-tax income (loss) from exited business		$ 879.2	$ 1,178.9	$ 352.3	$ 4,903.4

[1] Includes realized and unrealized gains (losses). See Note 3, Investments, for further details.