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Significant Transactions - Ark (Details) - USD ($) $ in Millions |  |  | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 01, 2021 | Oct. 01, 2020 | Sep. 30, 2022 | Sep. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2022 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020
Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Cash pre-funded/placed in escrow for Ark Transaction |  |  |  |  |  |  |  |  | $ 366.3
Other Operations |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Cash pre-funded/placed in escrow for Ark Transaction |  |  |  |  |  |  |  |  | 646.3
Goodwill and other intangible assets |  |  | $ 92.0 |  |  | $ 92.0 |  | $ 39.1 |
Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Goodwill and other intangible assets |  |  | 292.5 |  |  | 292.5 |  | 292.5 |
Contingent consideration |  |  | 32.9 |  |  | 32.9 |  | 28.0 |
Change in fair value of contingent consideration liabilities |  |  | 2.7 | $ 1.5 |  | 4.9 | $ 1.5 |  |
Ark | In-force Business Acquired |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Amortization |  |  | $ 0.7 | 11.0 |  | $ 6.8 | 54.9 |  |
Ark | Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 72.00% |  |  | 72.00% |  |  |
Fully diluted ownership interest (as a percent) |  |  | 63.00% |  |  | 63.00% |  |  |
Ark | Lloyd |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Cash pre-funded/placed in escrow for Ark Transaction |  |  |  |  |  |  |  |  | $ 280.0
Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Merger agreement, equity capital contributed | $ 605.4 |  |  |  |  |  |  |  |
Equity capital, pre money valuation amount |  | $ 300.0 |  |  |  |  |  |  |
Additional equity purchase from shareholders |  | 40.9 |  |  |  |  |  |  |
Investment, potential additional contribution of equity capital |  | $ 200.0 |  |  |  |  |  |  |
Assets acquired | 2,500.0 |  |  |  |  |  |  |  |
Goodwill and other intangible assets | 292.5 |  |  |  |  |  |  |  |
Liabilities acquired | 1,700.0 |  |  |  |  |  |  |  |
Contingent consideration | 22.5 |  |  |  |  |  |  |  |
Noncontrolling interest acquired | $ 220.2 |  |  |  |  |  |  |  |
Transaction costs |  |  |  |  | $ 25.3 |  |  |  |
Investment, potential additional contribution of equity capital terminated |  |  |  |  |  |  |  | $ 200.0 |
Ark | Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest (as a percent) |  |  | 72.00% |  |  | 72.00% |  | 72.00% |
Ark | Ark |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Fully diluted ownership interest (as a percent) |  |  | 63.00% |  |  | 63.00% |  | 63.00% |
Percent of outstanding shares after performance obligations are satisfied |  |  | 12.50% |  |  | 12.50% |  |  |
Ark | Group Ark Insurance Limited | Unsecured Subordinated Debt |  |  |  |  |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |  |  |  |  |
Notes issued |  |  |  | $ 163.3 |  |  | $ 163.3 |  |

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