Commitments and Contingencies - Employee and Office Lease Termination Costs (Detail) (Termination Costs [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Termination Costs [Member]
Expenses [Line Items]
Balance, beginning of period	$ 9.2	$ 11.9	$ 10.6	$ 13.6
Compensation expense	1.6	3.1	2.2	3.7
Contract termination costs		0.4	0.1	0.3
Costs paid or settled	(1.6)	(1.4)	(3.7)	(3.6)
Balance, end of period	$ 9.2	$ 14.0	$ 9.2	$ 14.0