Income Taxes - Schedule Of Provision For Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Current income taxes, Federal	$ 207.0	$ 148.7	$ 150.5
Current income taxes, State	13.4	8.4	7.0
Current income taxes, Foreign	5.4	7.6	7.5
Current income taxes	225.8	164.7	165.0
Deferred income taxes, Federal	18.3	7.5	(30.9)
Deferred income taxes, State	0.6	0.5	(0.6)
Deferred income taxes, Foreign	0.2	(3.0)	(3.3)
Deferred income taxes	19.1	5.0	(34.8)
Total income tax expense	$ 244.9	$ 169.7	$ 130.2