Information Related to Vesting of Performance Based Restricted Stock (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Tax benefit realized upon exercise	$ 26.0	$ 43.2	$ 41.1
Performance Based Restricted Stock [Member]
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award Performance Options [Line Items]
Fair value of vested shares	43.1	38.0	25.5
Tax benefit realized upon exercise	$ 15.6	$ 14.4	$ 9.7