Income Taxes - Schedule of Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate	$ (35.1)	$ (4.1)	$ (25.7)	$ (11.0)
Tax effect of:
Nontaxable investment income	0.0	0.0	(0.2)	(0.1)
Foreign exchange adjustments	0.0	0.0	0.0	(2.6)
Base Erosion and Anti-Abuse Tax	0.0	20.4	0.0	16.9
Withholding taxes	0.0	0.0	0.0	0.1
Ireland Capital Loss	0.0	0.0	3.3	0.0
U.S. state tax expense, net of federal income tax effect	0.0	0.0	0.0	(1.2)
Change in uncertain tax position liability	0.0	0.2	0.0	1.2
Change in valuation allowance	0.3	0.0	(2.2)	0.1
Impact of change in tax rate related to Finance Act 2021	0.0	0.0	0.0	(0.4)
Prior period adjustment	(0.3)	0.2	(3.6)	0.1
Other	0.7	0.9	1.2	0.2
Income tax provision (benefit)	$ (34.4)	$ 17.6	$ (27.2)	$ 3.3