Segment information - Information About Unconsolidated Equity Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
Carrying value of investments at year end	$ 4.9	$ 5.0	$ 4.9
Undistributed earnings	3.1	3.2	3.5
Share in earnings of equity method affiliates	0.8	0.9	1.9
Rest of World | Reportable Segments
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
Carrying value of investments at year end	4.5	4.4	4.2
Undistributed earnings	2.7	2.6	2.8
Share in earnings of equity method affiliates	0.7	0.6	0.9
Latin America | Reportable Segments
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
Carrying value of investments at year end	0.4	0.6	0.7
Undistributed earnings	0.4	0.6	0.7
Share in earnings of equity method affiliates	$ 0.1	$ 0.3	$ 1.0