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Fixed Assets - Summary of Fixed Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property Plant and Equipment Useful Life and Values [Abstract]
Office equipment	$ 28.6	$ 22.5
Furniture and fixtures	112.3	96.7
Leasehold improvements	124.2	107.8
Computer equipment	147.9	131.4
Land and buildings - corporate headquarters	143.6	141.7
Software	291.9	268.4
Other	12.0	10.0
Work in process	20.1	10.6
Gross fixed assets	880.6	789.1
Accumulated depreciation	(468.4)	(411.5)
Net fixed assets	$ 412.2	$ 377.6

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Property Plant and Equipment Useful Life and Values [Abstract]

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Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

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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.

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Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.

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Amount before accumulated depreciation of additions or improvements to assets held under a lease arrangement.

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Amount before accumulated depreciation of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment.

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