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Acquisitions and Dispositions of Businesses - Completed Acquisitions Narrative (Details) - acquisition | 3 Months Ended | 6 Months Ended |  |  |  |
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Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Apr. 06, 2020 | Jan. 31, 2020 | Jan. 03, 2020 | Jan. 01, 2020
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Number of business acquired under business combination | 0 | 1 | 0 | 6 |  |  |  |
Farmington Administrative Services LLC |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  | 100.00% |  |  |
Cytelligence Inc. |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  | 100.00% |  |
Cover Wallet Inc. |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  | 100.00% |
TRIUM GmbH Insurance Broker |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  | 100.00%
Assimedia SA |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  | 100.00%
Apollo Conseil et Courtage |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Percentage of capital acquired |  |  |  |  |  |  |  | 100.00%

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- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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