Property and Equipment, Net (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Office and computer equipment (3 - 10 year estimated useful life)	$ 172.1	$ 152.5
Office furniture and fixtures (3 - 10 year estimated useful life)	45.4	43.8
Internal-use computer software (3 - 10 year estimated useful life)	387.0	336.8
Leasehold improvements (3 - 20 year estimated useful life)	220.8	220.7
Total property and equipment, at cost	825.3	753.8
Less: accumulated depreciation and amortization	(518.9)	(451.5)
Total property and equipment, net	$ 306.4	$ 302.3