Reinsurance - Components of Net Realized Capital Gains (Losses) on Funds Withheld Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Reinsurance
Net realized capital gains (losses)	$ 0.8	$ (13.1)	$ (49.6)	$ (52.5)
Fixed maturities, available-for-sale
Reinsurance
Net realized capital gains (losses)	1.3	(10.8)	(46.2)	(52.0)
Fixed maturities, trading
Reinsurance
Net realized capital gains (losses)			0.1
Mortgage loans
Reinsurance
Net realized capital gains (losses)	(0.1)	(1.8)	(1.4)	(1.8)
Derivatives
Reinsurance
Net realized capital gains (losses)	$ (0.4)	$ (0.5)	$ (2.1)	$ 1.3