Income taxes - Component of Income Taxes Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Currently payable:
U.S. federal and state	$ 16.3	$ 29.7	$ 13.3
Non-U.S.	20.1	21.5	14.9
Total	36.4	51.2	28.2
Deferred income taxes (benefit):
U.S. federal and state	(3.9)	(1.7)	(10.3)
Non-U.S.	1.3	10.6	(2.0)
Total	(2.6)	8.9	(12.3)
Income tax expense	$ 33.8	$ 60.1	$ 15.9