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Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) $ in Millions | 9 Months Ended
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Sep. 30, 2019 USD ($)
Goodwill [Line Items] |
Beginning Balance | $ 4,625.6
Goodwill acquired during the period | 756.1
Goodwill adjustments due to appraisals and other acquisition adjustments | (1.8)
Goodwill written-off related to sales of business | (7.2)
Foreign currency translation adjustments during the period | (57.9)
Ending Balance | 5,314.8
Brokerage [Member] |
Goodwill [Line Items] |
Beginning Balance | 4,573.6
Goodwill acquired during the period | 738.8
Goodwill adjustments due to appraisals and other acquisition adjustments | (1.3)
Goodwill written-off related to sales of business | (7.2)
Foreign currency translation adjustments during the period | (57.1)
Ending Balance | 5,246.8
Risk Management [Member] |
Goodwill [Line Items] |
Beginning Balance | 49.3
Goodwill acquired during the period | 16.9
Goodwill adjustments due to appraisals and other acquisition adjustments | (0.5)
Foreign currency translation adjustments during the period | (0.8)
Ending Balance | 64.9
Corporate [Member] |
Goodwill [Line Items] |
Beginning Balance | 2.7
Goodwill acquired during the period | 0.4
Ending Balance | $ 3.1

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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- Definition Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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- Definition Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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