Lease Commitments - Additional Information (Detail) In Millions, unless otherwise specified	12 Months Ended				0 Months Ended	12 Months Ended	0 Months Ended			12 Months Ended	0 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Oct. 21, 2013 USD ($)	Mar. 28, 2007 7WTC	Dec. 31, 2013 7WTC USD ($) years	Oct. 21, 2013 Six Floors In Canary Wharf District years	Dec. 31, 2013 Six Floors In Canary Wharf District USD ($)	Dec. 31, 2013 Six Floors In Canary Wharf District GBP (£)	Dec. 31, 2013 Computer and other equipment	Oct. 21, 2013 3 Additional floors
Lease Commitments And Contingencies [Line Items]
Rent and amortization expenses under operating leases	$ 74.2	$ 75.8	$ 73.1
Expiration of operating lease (in years)	14 years									4 years
Operating lease, period of lease, in years						21	17.5
Renewal options, years						20 years
Additional Floors					20 years						14 years
Total base rent	805.6			74.0					134.0
Remaining rent obligation						558.1		181.4
Capital lease future minimum sublease rentals	$ 7.1