Leases - Supplemental balance sheet (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease assets	$ 322.0	$ 270.3
Finance lease assets	$ 169.5	$ 162.5
Finance lease, right-of-use asset, statement of financial position [extensible list]	us-gaap:PropertyPlantAndEquipmentNet	us-gaap:PropertyPlantAndEquipmentNet
Total lease assets	$ 491.5	$ 432.8
Current liabilities operating leases	$ 77.2	$ 65.9
Operating lease, liability, current, statement of financial position [extensible list]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Current liabilities financing leases	$ 37.5	$ 32.5
Finance lease, liability, current, statement of financial position [extensible list]	us-gaap:LongTermDebtCurrent	us-gaap:LongTermDebtCurrent
Lease liabilities	$ 267.2	$ 218.4
Noncurrent liabilities financing leases	$ 113.9	$ 117.0
Finance lease, liability, noncurrent, statement of financial position [extensible list]	us-gaap:LongTermDebtNoncurrent	us-gaap:LongTermDebtNoncurrent
Total lease liabilities	$ 495.8	$ 433.8