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Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Beginning balance | $ 525.5 | $ 525.5 |  |
Amortization |  | (39.8) | $ (28.3) | $ (21.8)
Impairments |  | (30.2) | 0.0 |
Ending balance |  | 645.5 | 525.5 |
J.C. Taylor Insurance |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 27.2 |  |
Kingsbridge Group Limited |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  |  | 13.6 |
Measurement period adjustments |  |  | 4.1 |
Other Operations |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 9.3 | 9.6 |
Fresh Insurance Services Group Limited |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Proceeds from sale of other assets | 1.5 |  |  |
Goodwill |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Beginning balance | 525.5 | 525.5 | 394.7 |
Acquisition of businesses |  | 71.5 | 140.0 |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | (36.5) | (23.2) |
Measurement period adjustments |  | (0.1) | 0.6 |
Disposition of businesses |  | 0.0 | 0.0 |
Amortization |  | 0.0 | 0.0 |
Impairments |  | 0.0 | 0.0 |
Assets held for sale |  |  | 0.0 |
Loss on assets held for sale |  | (30.2) | 0.0 |
Foreign currency translation |  | (1.5) | 13.4 |
Ending balance |  | 645.5 | 525.5 | 394.7
Goodwill | Ark |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Ark Transaction |  | 116.8 | 0.0 |
Goodwill | J.C. Taylor Insurance |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquisition of businesses |  | 55.7 |  |
Goodwill | Kingsbridge Group Limited |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquisition of businesses |  |  | 125.1 |
Goodwill | Other Operations |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquisition of businesses |  |  | 14.9 |
Goodwill | Other Operations |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Acquisition of businesses |  | 15.8 |  |
Total other intangible assets |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Beginning balance | 256.9 | 256.9 | 260.0 |
Acquisition of businesses |  | 0.0 | 0.0 |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 36.5 | 23.2 |
Measurement period adjustments |  | 0.0 | 6.6 |
Disposition of businesses |  | 0.0 | 0.0 |
Amortization |  | (39.8) | (28.3) |
Impairments |  | 0.0 | (6.2) |
Assets held for sale |  | (8.6) | 0.0 |
Loss on assets held for sale |  | 0.0 | 0.0 |
Foreign currency translation |  | (0.3) | 1.6 |
Ending balance |  | 420.4 | 256.9 | 260.0
Total other intangible assets | Ark |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Ark Transaction |  | 175.7 | 0.0 |
Total Goodwill and Other Intangible Assets |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Beginning balance | $ 782.4 | 782.4 | 654.7 |
Acquisition of businesses |  | 71.5 | 140.0 |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 0.0 | 0.0 |
Measurement period adjustments |  | (0.1) | 7.2 |
Disposition of businesses |  | 0.0 | 0.0 |
Amortization |  | (39.8) | (28.3) |
Impairments |  | 0.0 | (6.2) |
Assets held for sale |  | (8.6) | 0.0 |
Loss on assets held for sale |  | (30.2) | 0.0 |
Foreign currency translation |  | (1.8) | 15.0 |
Ending balance |  | 1,065.9 | 782.4 | $ 654.7
Total Goodwill and Other Intangible Assets | Ark |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Ark Transaction |  | $ 292.5 | $ 0.0 |

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