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Unpaid Losses And Loss Adjustment Expenses (Prior Year Losses and Loss Adjustment Expenses Development by Product Line) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | $ (455.3) | $ (38.6) | $ (167.4)
Insurance [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (451.0) | (104.7) | (142.9)
Insurance [Member] | Professional liability [Member] | U.S. [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | 111.8 | 56.8 |
Insurance [Member] | Professional liability [Member] | International |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (152.6) | (102.2) |
Insurance [Member] | Professional liability [Member] | Short-Duration Insurance Contracts, Accident Years 2018 and 2019 |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  |  | 121.0
Insurance [Member] | Professional liability [Member] | Short-Duration Insurance Contracts, Accident Years, all other |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  |  | (91.1)
Insurance [Member] | General liability [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (81.6) |  |
Insurance [Member] | General liability [Member] | U.S. [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  | 274.0 |
Insurance [Member] | General liability [Member] | International |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  | (36.5) |
Insurance [Member] | General liability [Member] | Short-Duration Insurance Contracts, Accident Years 2016 to 2019 |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  |  | 61.6
Insurance [Member] | General liability [Member] | Short-Duration Insurance Contracts, Accident Years, all other |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  |  | (20.5)
Insurance [Member] | Property [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (75.0) | (95.1) | (48.1)
Insurance [Member] | Marine and energy [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (58.3) | (76.5) |
Insurance [Member] | Personal Lines |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  | (42.8) |
Insurance [Member] | Workers' compensation [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  | (36.5) | (62.1)
Insurance [Member] | Programs [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (53.9) |  | (48.3)
Insurance [Member] | Credit and surety [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (51.4) |  | (31.7)
Insurance [Member] | Other products [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (90.0) | (45.9) | (23.7)
Reinsurance [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (12.3) | 57.1 | (26.1)
Reinsurance [Member] | Professional liability [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (17.1) |  |
Reinsurance [Member] | General liability [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  | 95.5 |
Reinsurance [Member] | Property [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (23.0) | (21.6) | (29.2)
Reinsurance [Member] | Workers' compensation [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (20.3) | (14.9) |
Reinsurance [Member] | Premium adjustments |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | (4.0) | 11.4 | 53.1
Reinsurance [Member] | Credit and surety [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years |  |  | (22.9)
Reinsurance [Member] | Public entity |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | 34.1 | 53.7 |
Reinsurance [Member] | Other products [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | 18.0 | (67.0) | (27.1)
Other [Member] | Other underwriting [Member] |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Incurred losses and loss adjustment expenses, prior accident years | $ 8.0 | $ 9.0 | $ 1.6

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