Leases and commitments - Maturities of Lease Liabilities, Topic 842 (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finance Leases
2021	$ 2.6
2022	2.0
2023	0.7
2024	0.4
2025	0.0
Thereafter	0.0
Total lease payments	5.7
Less imputed interest	0.2
Total	5.5	$ 5.3
Operating Leases
2021	40.8
2022	33.6
2023	19.6
2024	9.0
2025	4.4
Thereafter	0.8
Total lease payments	108.2
Less imputed interest	8.7
Total	$ 99.5	$ 90.1