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Significant Transactions - NSM (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Aug. 01, 2022 | Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Other Significant Noncash Transactions [Line Items] |  |  |  |  |
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group |  |  |  | $ 886.8 | $ 18.7
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group |  | $ 2.9 | $ 0.0 | 2.9 | 0.0
NSM Insurance Group |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group |  | $ 886.8 | $ 0.0 | $ 886.8 | $ 0.0
Discontinued Operations, Disposed of by Sale | NSM Insurance Group |  |  |  |  |
Other Significant Noncash Transactions [Line Items] |  |  |  |  |
Transaction value | $ 1,400.0 |  |  |  |
Gain on transaction | 875.7 |  |  |  |
Net gain (loss) from sale of discontinued operations, net of tax - Sirius Group | 886.8 |  |  |  |
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group | 2.9 |  |  |  |
Compensation and other costs | $ 14.0 |  |  |  |

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