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Goodwill and Other Intangible Assets - Schedule of Acquisition Date Fair Values, Accumulated Amortization and Net Carrying Values for Other Intangibles Assets and Goodwill, By Company (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2022 | Mar. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, acquisition date fair value | $ 671.6 |  | $ 675.7 |
Goodwill, impairments | 30.2 |  | 30.2 |
Goodwill, net carrying value | 641.4 |  | 645.5 |
Goodwill |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, impairments | 0.0 | $ 30.2 |  |
Goodwill, net carrying value | 641.4 | 613.4 | 645.5 | $ 525.5
Goodwill, foreign currency translation gain (loss) | (4.1) | 1.5 |  |
Other |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, impairments | 0.0 | 0.0 |  |
Other intangible assets, foreign currency translation gain (loss) | (0.2) | $ 0.2 |  |
Total Equity Including Noncontrolling Interest |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, acquisition date fair value | 1,191.5 |  | 1,196.1 |
Other intangible assets, accumulated amortization | 103.6 |  | 93.8 |
Impairment of intangible assets, including goodwill | 36.4 |  | 36.4 |
Goodwill and other intangible assets | 1,051.5 |  | 1,065.9 |
Non-controlling interest |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill and other intangible assets | 117.1 |  | 117.6 |
Total |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill and other intangible assets | 934.4 |  | 948.3 |
Other |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, acquisition date fair value | 519.9 |  | 520.4 |
Other intangible assets, accumulated amortization | 103.6 |  | 93.8 |
Other intangible assets, impairments | 6.2 |  | 6.2 |
Other intangible assets, net carrying value | 410.1 |  | 420.4 |
Ark |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, acquisition date fair value | 116.8 |  | 116.8 |
Goodwill, impairments | 0.0 |  | 0.0 |
Goodwill, net carrying value | 116.8 |  | 116.8 |
Ark | Trade names |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, acquisition date fair value | 175.7 |  | 175.7 |
Other intangible assets, accumulated amortization | 0.0 |  | 0.0 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | 175.7 |  | 175.7 |
Specialty Insurance Distribution (NSM) |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, acquisition date fair value | 529.3 |  | 533.4 |
Goodwill, impairments | 30.2 |  | 30.2 |
Goodwill, net carrying value | 499.1 |  | 503.2 |
Other intangible assets, acquisition date fair value | 314.7 |  | 315.2 |
Other intangible assets, accumulated amortization | 95.6 |  | 86.8 |
Other intangible assets, impairments | 6.2 |  | 6.2 |
Other intangible assets, net carrying value | 212.9 |  | 222.2 |
Specialty Insurance Distribution (NSM) | Goodwill |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, foreign currency translation gain (loss) | (4.1) |  |  |
Other intangible assets, foreign currency translation gain (loss) | (0.5) |  |  |
Specialty Insurance Distribution (NSM) | Other |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, foreign currency translation gain (loss) | $ 0.3 |  |  |
Specialty Insurance Distribution (NSM) | Customer relationships |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 9 years 2 months 12 days |  |  |
Other intangible assets, acquisition date fair value | $ 159.4 |  | 159.9 |
Other intangible assets, accumulated amortization | 62.3 |  | 57.0 |
Other intangible assets, impairments | 3.5 |  | 3.5 |
Other intangible assets, net carrying value | $ 93.6 |  | 99.4 |
Specialty Insurance Distribution (NSM) | Trade names |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 18 years |  |  |
Other intangible assets, acquisition date fair value | $ 68.5 |  | 68.6 |
Other intangible assets, accumulated amortization | 12.9 |  | 11.9 |
Other intangible assets, impairments | 1.0 |  | 1.0 |
Other intangible assets, net carrying value | 54.6 |  | 55.7 |
Specialty Insurance Distribution (NSM) | Information technology platform |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, acquisition date fair value | 3.1 |  | 3.1 |
Other intangible assets, accumulated amortization | 1.4 |  | 1.4 |
Other intangible assets, impairments | 1.7 |  | 1.7 |
Other intangible assets, net carrying value | $ 0.0 |  | 0.0 |
Specialty Insurance Distribution (NSM) | Renewal rights |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 12 years |  |  |
Other intangible assets, acquisition date fair value | $ 82.5 |  | 82.5 |
Other intangible assets, accumulated amortization | 18.3 |  | 15.8 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | $ 64.2 |  | 66.7 |
Specialty Insurance Distribution (NSM) | Other |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 3 years 3 months 18 days |  |  |
Other intangible assets, acquisition date fair value | $ 1.2 |  | 1.1 |
Other intangible assets, accumulated amortization | 0.7 |  | 0.7 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | 0.5 |  | 0.4 |
Asset Management (Kudu) |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, acquisition date fair value | 7.6 |  | 7.6 |
Goodwill, impairments | 0.0 |  | 0.0 |
Goodwill, net carrying value | $ 7.6 |  | 7.6 |
Asset Management (Kudu) | Trade names |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 7 years |  |  |
Other intangible assets, acquisition date fair value | $ 2.2 |  | 2.2 |
Other intangible assets, accumulated amortization | 0.9 |  | 0.9 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | 1.3 |  | 1.3 |
Other Operations |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill, acquisition date fair value | 17.9 |  | 17.9 |
Goodwill, impairments | 0.0 |  | 0.0 |
Goodwill, net carrying value | 17.9 |  | 17.9 |
Other intangible assets, acquisition date fair value | 27.3 |  | 27.3 |
Other intangible assets, accumulated amortization | 7.1 |  | 6.1 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | $ 20.2 |  | 21.2 |
Other Operations | Customer relationships |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 13 years |  |  |
Other intangible assets, acquisition date fair value | $ 18.8 |  | 18.8 |
Other intangible assets, accumulated amortization | 5.2 |  | 4.5 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | $ 13.6 |  | 14.3 |
Other Operations | Trade names |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 17 years 6 months |  |  |
Other intangible assets, acquisition date fair value | $ 8.2 |  | 8.2 |
Other intangible assets, accumulated amortization | 1.7 |  | 1.5 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | $ 6.5 |  | 6.7 |
Other Operations | Other |  |  |  |
Acquired Finite-Lived Intangible Assets [Line Items] |  |  |  |
Other intangible assets, weighted average useful life (in years) | 5 years 3 months 18 days |  |  |
Other intangible assets, acquisition date fair value | $ 0.3 |  | 0.3 |
Other intangible assets, accumulated amortization | 0.2 |  | 0.1 |
Other intangible assets, impairments | 0.0 |  | 0.0 |
Other intangible assets, net carrying value | $ 0.1 |  | $ 0.2 |

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