Income Taxes - Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax at Statutory Rate	$ 411.1	$ 571.9	$ 531.0
Tax Exempt Income	(6.9)	(9.6)	(7.2)
Foreign Tax Rate Differential	(7.3)	(50.0)	(50.9)
Excess Tax Benefit Related to Share-Based Compensation	(16.8)	(31.6)	(12.3)
State Taxes, net	65.5	41.0	31.1
Impact of Tax Cuts and Jobs Act	(4.8)	(53.1)	0.0
Change in Accounting Method	24.4	0.0	0.0
Other	(15.0)	(33.7)	(7.1)
Provision for Income Taxes	$ 401.4	$ 434.9	$ 484.6