Other Income, Net - Schedule of Components of Other Income (Detail) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Securities earnings:
Dividends and interest						$ 4.8	$ 10.9	$ 26.1
Securities transactions, net						(0.1)	0.3	12.4
Total						4.7	11.2	38.5
Gain on land sales	$ 4.0			$ 4.4		4.5	4.4	12.5
Gain on sale of business			$ 3.0			4.9	3.0	58.4
Insurance recoveries					$ 7.7	1.6	7.7	1.3
Currency transactions, net						(4.0)	2.0	10.1
Disposal of property and equipment, net						(0.2)	(0.3)	(0.3)
Infrastructure reimbursement		$ 19.1			$ 8.8	19.7	9.2	4.3
Other, net						2.1	3.7	2.8
Total						$ 28.4	$ 40.9	$ 69.2