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Fixed Assets - Summary of Fixed Assets (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Property Plant And Equipment Useful Life And Values [Abstract] |  |
Office equipment | $ 33.0 | $ 32.6
Furniture and fixtures | 138.3 | 126.0
Leasehold improvements | 166.0 | 150.2
Computer equipment | 214.2 | 176.3
Land and buildings - corporate headquarters | 145.1 | 144.9
Software | 452.2 | 392.3
Other | 16.7 | 19.0
Work in process | 14.1 | 18.0
Gross fixed assets | 1,179.6 | 1,059.3
Accumulated depreciation | (728.9) | (591.9)
Net fixed assets | $ 450.7 | $ 467.4

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- Definition Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.14) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 985 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756 + Details
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- Definition Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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