Leases and commitments - Supplemental Cash Flow Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Cash payments for operating leases included in operating activities	$ 73.2
Cash payments for finance leases included in financing activities	1.7
Cash payments for finance lease included in operating activities	0.3
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	69.6
Finance leases	$ 1.5