Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets related to:
Non-U.S. net operating loss carryforwards	$ 62.8	$ 68.2
Intangible assets	51.5	51.5
Incentive compensation	23.8	25.4
Unearned premiums	20.5	18.2
Loss reserves	8.5	8.4
U.S. federal and state net operating and capital loss carryforwards	6.4	87.6
Tax credit carryforwards	2.8	3.3
Accrued interest	0.2	10.1
Deferred acquisition costs	0.0	3.7
Other items	0.9	1.0
Total gross deferred tax assets	177.4	277.4
Less: valuation allowances	89.2	116.1
Total net deferred tax assets	88.2	161.3
Deferred tax liabilities related to:
Purchase accounting	43.9	43.9
Investment basis difference	43.5	40.9
Deferred underwriting	24.3	18.3
Net unrealized investment gains	19.0	15.5
Deferred acquisition costs	6.5	0.0
BAM member surplus contributions prior to deconsolidation	0.0	82.2
Other items	1.2	1.2
Total deferred tax liabilities	138.4	202.0
Net deferred tax asset (liability)	$ (50.2)	$ (40.7)