Restricted Stock Units - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Payments Disclosure [Line Items]
Stock units granted, ratable vesting period	5 years
Description of vesting term for awards granted	Awards granted under the plan generally vest ratably over a period of five years beginning on the first anniversary of the grant date or in full on the fifth anniversary of the grant date.
Restricted Stock Units
Share Based Payments Disclosure [Line Items]
Compensation expense from the vesting of restricted stock units	$ 39.6	$ 56.1	$ 54.2
Weighted average grant date fair value for restricted stock units granted (usd per share)	$ 49.76	$ 57.95	$ 47.72
Unrecognized restricted stock units compensation expense	$ 68.2
Unrecognized restricted stock units compensation expense, weighted average recognition period	1 year 10 months