Segment Information - Revenues from exited business (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Revenues from exited business:
Change in fair value of funds withheld embedded derivative		$ (626.6)	$ 0.0
Net realized capital gains (losses) on funds withheld assets	[1]	81.0
Total revenues from exited business		(547.6)
Reconciling Items
Revenues from exited business:
Change in fair value of funds withheld embedded derivative		(626.6)
Net realized capital gains (losses) on funds withheld assets		81.0
Amortization of reinsurance gain		1.4
Other impacts of reinsured business		(3.4)
Total revenues from exited business		$ (547.6)

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