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Related Party Transactions (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Related Party Transaction [Line Items] |  |  |
Other assets | $ 700.0 | $ 597.0 |
Other liabilities | 435.0 | 457.0 |
Related Party |  |  |
Related Party Transaction [Line Items] |  |  |
Management fee expense | 1.9 | 2.0 | $ 2.4
Accounts payable | $ 1.0 | $ 1.0 |
Wellington Management Company LLP |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership percentage by noncontrolling owners | 5.00% | 5.00% |
BlackRock Financial Management Inc. |  |  |
Related Party Transaction [Line Items] |  |  |
Ownership percentage by noncontrolling owners | 5.00% | 5.00% |

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