Property and Equipment, Net (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Office and computer equipment (3 - 10 year estimated useful life)	$ 189.1	$ 172.1
Office furniture and fixtures (3 - 10 year estimated useful life)	47.1	45.4
Internal-use computer software (3 - 10 year estimated useful life)	452.1	387.0
Leasehold improvements (3 - 20 year estimated useful life)	233.1	220.8
Total property and equipment, at cost	921.4	825.3
Less: accumulated depreciation and amortization	(595.5)	(518.9)
Total property and equipment, net	$ 325.9	$ 306.4