Income Taxes - Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax at Statutory Rate	$ 571.9	$ 531.0	$ 512.7
Tax Exempt Income	(9.6)	(7.2)	(4.8)
Foreign Tax Rate Differential	(50.0)	(50.9)	(44.2)
Excess Tax Benefit Related to Share-Based Compensation	(31.6)	(12.3)	0.0
State Taxes, net	41.0	31.1	33.1
Impact of Tax Cuts and Jobs Act	(53.1)	0.0	0.0
Other	(33.7)	(7.1)	(5.6)
Provision for Income Taxes	$ 434.9	$ 484.6	$ 491.2