Property and Equipment, Net (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Office and computer equipment (3 - 20 year estimated useful life)	$ 119.7	$ 106.8
Office furniture and fixtures (5 - 10 year estimated useful life)	40.3	40.6
Internal-use computer software (3 - 5 year estimated useful life)	263.9	241.8
Leasehold improvements (3 - 20 year estimated useful life)	197.5	195.8
Total property and equipment, at cost	621.4	585.0
Less: accumulated depreciation and amortization	(314.3)	(258.2)
Total property and equipment, net	$ 307.1	$ 326.8