Stock-Based Compensation Cost and Associated Tax Benefit (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Compensation Related Costs Share Based Payments Disclosure [Line Items]
Stock compensation cost	$ 22.1	$ 19.3	$ 66.5	$ 59.9
Tax benefit	$ 7.2	$ 6.2	$ 21.8	$ 19.0