Basis of Presentation and Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) segment	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	May 26, 2022	May 25, 2022	Jan. 01, 2021 USD ($)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of reportable segments | segment	4
Other long-term investments	$ 2,150.2	$ 1,998.2
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Operating lease, right-of-use asset	$ 32.6	$ 20.3
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other liabilities	Other liabilities
Lease liabilities	$ 35.5	$ 22.0
Net unrealized gains (losses) from foreign currency translation	(1.7)	(1.6)
Change in fair value of contingent consideration - Ark	61.3	48.7	$ 17.3
P&C Insurance and Reinsurance (Ark/WM Outrigger) | Operating Segments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	547.8	440.9
Contingent consideration	155.3	94.0				$ 22.5
Change in fair value of contingent consideration - Ark	$ 61.3	48.7	$ 17.3
Third Point Re | P&C Insurance and Reinsurance (Ark/WM Outrigger)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Annual crediting rate	3.00%
Level 2
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Variance threshold for outliers	$ 0.5
Variance threshold for outliers (as a percent)	5.00%
Level 2 | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	$ 23.5	26.2
Level 3 | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	1,262.7	1,138.2
NAV | Fair value measured on a recurring basis | Other long-term investments
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other long-term investments	864.0	$ 833.8
Subsidiary - HG Global
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Purchase of surplus notes	$ 503.0
Subsidiary - HG Global | Maximum
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percentage of par value of policy reinsured	15.00%
Ark
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percent of shares outstanding	12.30%
Subsidiary - Ark Insurance Holdings Limited
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	72.10%	72.00%
Ownership percentage, after equity incentives	61.90%	61.90%
Subsidiary - WM Outrigger Re | Preferred stocks
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	100.00%	100.00%
Subsidiary - HG Global | Preferred stocks
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	96.90%	96.90%
Subsidiary - HG Global | Common Stock
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	88.40%	88.40%
Kudu
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	90.40%
Ownership percentage basic units outstanding		89.60%		89.30%	99.10%
Ownership percentage, fully diluted	77.00%
Ownership percentage, fully converted		76.30%
Bamboo
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Basic ownership	72.80%
Ownership percentage, fully diluted	63.70%