Reserve for Claims and Claim Expenses - Schedule of Claims and Claim Expense Reserves by Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	$ 5,262,596	$ 3,821,053
Additional Case Reserves	1,662,570	2,176,884
IBNR	13,561,703	9,894,636
Total reserve for claims and claim expenses	20,486,869	15,892,573	$ 13,294,630
Validus
Liability for Claims and Claims Adjustment Expense [Line Items]
Total reserve for claims and claim expenses	4,500,000
Property | Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	2,461,580	1,956,688
Additional Case Reserves	1,459,010	2,008,891
IBNR	3,913,030	3,570,253
Total reserve for claims and claim expenses	7,833,620	7,535,832
Casualty and Specialty | Operating Segments
Liability for Claims and Claims Adjustment Expense [Line Items]
Case Reserves	2,801,016	1,864,365
Additional Case Reserves	203,560	167,993
IBNR	9,648,673	6,324,383
Total reserve for claims and claim expenses	$ 12,653,249	$ 8,356,741