CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Common shares, par value per share (in dollars per share)	$ 1	$ 1
Common shares, authorized shares (in shares)	50,000,000	50,000,000
Common shares, issued shares (in shares)	2,568,148	2,560,452
Common shares, outstanding shares (in shares)	2,568,148	2,560,452
Operating Segments | P&C Insurance and Reinsurance (Ark/WM Outrigger)
Restricted cash	$ 14.1	$ 0.7
Operating Segments | Bamboo
Restricted cash	$ 59.5	$ 0.0