Other Income, Net - Schedule of Components of Other Income (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Securities earnings:
Dividends and interest				$ 21.6	$ 20.3
Securities transactions, net				0.1	0.2
Total		$ 7.5	$ 6.8	21.7	20.5
Currency transactions, net				(8.0)	3.2
Insurance recoveries		0.1	0.1	0.2	0.4
Business interruption insurance proceeds					3.4
Termination fee	$ 4.0			4.0
Other, net				1.9	0.8
Total		$ 4.5	$ 6.2	$ 19.8	$ 28.3