Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets related to:
Non-U.S. net operating loss carryforwards	$ 63.1	$ 62.8
Incentive compensation	29.3	23.8
U.S. federal and state net operating and capital loss carryforwards	15.4	6.4
Accrued interest	6.0	0.2
Tax credit carryforwards	3.7	2.8
Intangible assets	0.4	51.5
Unearned premiums	0.0	20.5
Loss reserves	0.0	8.5
Other items	1.6	0.9
Total gross deferred tax assets	119.5	177.4
Less: valuation allowances	95.8	89.2
Total net deferred tax assets	23.7	88.2
Deferred tax liabilities related to:
Investment basis difference	87.7	43.5
Purchase accounting	43.9	43.9
Deferred underwriting	27.5	24.3
Net unrealized investment gains	22.2	19.0
Deferred acquisition costs	0.0	6.5
Other items	2.0	1.2
Total deferred tax liabilities	183.3	138.4
Net deferred tax asset (liability)	$ (159.6)	$ (50.2)