Income Taxes - Components of Earnings Before Income Taxes and Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
United States	$ 524.4	$ 388.4	$ 337.6
Foreign, principally Australia, Canada, New Zealand and the U.K.	346.5	237.7	141.8
Earnings before income taxes	870.9	626.1	479.4
Federal Current	43.6	3.8
Federal Deferred	(112.4)	(142.5)	(214.0)
Total Provision (benefit) for income taxes, Federal	(68.8)	(138.7)	(214.0)
State and local Current	36.6	11.1	15.4
State and local Deferred	(19.3)	(6.0)	(29.0)
Total Provision (benefit) for income taxes, State and local	17.3	5.1	(13.6)
Foreign Current	94.6	66.6	60.7
Foreign Deferred	(30.3)	(22.7)	(29.6)
Total Provision (benefit) for income taxes, Foreign	64.3	43.9	31.1
Total provision (benefit) for income taxes	$ 12.8	$ (89.7)	$ (196.5)