Income Taxes - Components of Earnings Before Income Taxes and Provision for Income Taxes (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
United States									$ 388.4	$ 337.6	$ 274.1
Foreign, principally Australia, Canada, New Zealand and the U.K.									237.7	141.8	85.7
Earnings before income taxes	$ 84.0	$ 114.8	$ 105.5	$ 321.8	$ 43.2	$ 90.3	$ 103.6	$ 242.3	626.1	479.4	359.8
Federal Current									3.8		7.1
Federal Deferred									(142.5)	(214.0)	(183.5)
Total Provision (benefit) for income taxes, Federal									(138.7)	(214.0)	(176.4)
State and local Current									11.1	15.4	11.6
State and local Deferred									(6.0)	(29.0)	(3.9)
Total Provision (benefit) for income taxes, State and local									5.1	(13.6)	7.7
Foreign Current									66.6	60.7	25.9
Foreign Deferred									(22.7)	(29.6)	(14.3)
Total Provision (benefit) for income taxes, Foreign									43.9	31.1	11.6
Benefit for income taxes									$ (89.7)	$ (196.5)	$ (157.1)