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Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Goodwill, beginning balance |  | $ 525.5 |  | $ 525.5 |  |
Goodwill, impairment loss |  |  |  | (30.2) |  | $ 0.0
Amortization of other intangible assets | $ (8.7) |  | $ (6.6) | (17.9) | $ (11.7) |
Goodwill, ending balance | 629.4 |  |  | 629.4 |  | 525.5
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] |  |  |  |  |  |
Goodwill, beginning balance | 613.4 | 525.5 | 392.4 | 525.5 | 394.7 | 394.7
Acquisitions of businesses | 15.8 |  | 125.1 | 15.8 | 125.1 |
Goodwill, foreign currency translation gain (loss) | 0.2 |  | 0.7 | 1.7 | (1.8) |
Impairments | 0.0 |  | 0.0 | 0.0 | 0.0 |
Goodwill, impairment loss |  |  |  | (30.2) | 0.0 |
Measurement period adjustments |  |  |  | (0.2) | 0.2 |
Amortization of other intangible assets | 0.0 |  | 0.0 | 0.0 | 0.0 |
Goodwill, ending balance | 629.4 | 613.4 | 518.2 | 629.4 | 518.2 | 525.5
Goodwill | Ark |  |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Goodwill acquired |  |  |  | 116.8 | 0.0 |
Other Intangible Assets |  |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Other intangible assets (excluding goodwill), beginning balance | 423.6 | 256.9 | 254.4 | 256.9 | 260.0 | 260.0
Acquisitions of businesses | 0.0 |  | 0.0 | 0.0 | 0.0 |
Other intangible assets, foreign currency translation gain (loss) | (0.1) |  | 0.1 | 0.1 | (0.4) |
Impairments | 0.0 |  | (6.2) | 0.0 | (6.2) |
Goodwill, impairment loss |  |  |  | 0.0 | 0.0 |
Measurement period adjustments |  |  |  | 0.0 | 0.0 |
Amortization of other intangible assets | (8.7) |  | (6.6) | (17.9) | (11.7) |
Other intangible assets (excluding goodwill), ending balance | 414.8 | 423.6 | 241.7 | 414.8 | 241.7 | 256.9
Other Intangible Assets | Ark |  |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Intangible assets acquired |  |  |  | 175.7 | 0.0 |
Total Goodwill and Other Intangible Assets |  |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Other intangible assets, gross (including goodwill), beginning balance | 1,037.0 | 782.4 | 646.8 | 782.4 | 654.7 | 654.7
Acquisitions of businesses | 15.8 |  | 125.1 | 15.8 | 125.1 |
Other intangible assets, foreign currency translation gain (loss) | 0.1 |  | 0.8 | 1.8 | (2.2) |
Impairments | 0.0 |  | (6.2) | 0.0 | (6.2) |
Goodwill, impairment loss |  |  |  | (30.2) | 0.0 |
Measurement period adjustments |  |  |  | (0.2) | 0.2 |
Amortization of other intangible assets | (8.7) |  | (6.6) | (17.9) | (11.7) |
Other intangible assets, gross (including goodwill), ending balance | $ 1,044.2 | $ 1,037.0 | $ 759.9 | 1,044.2 | 759.9 | $ 782.4
Total Goodwill and Other Intangible Assets | Ark |  |  |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |  |  |
Goodwill and other intangible assets acquired |  |  |  | $ 292.5 | $ 0.0 |

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