Leasing - Assets and liabilities, lessee (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Current liabilities:
Current portion of operating lease liabilities	$ 46.1	$ 47.4
Current portion of finance lease liabilities	23.0	20.9
Operating lease assets	154.7	157.3
Finance lease assets	76.5	69.5
Total lease assets	231.2	226.8
Noncurrent liabilities:
Operating lease liabilities	116.4	114.5
Finance lease liabilities	55.5	50.3
Total lease liabilities	$ 241.0	$ 233.1
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet	us-gaap:PropertyPlantAndEquipmentNet
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherAccruedLiabilitiesCurrent	us-gaap:OtherAccruedLiabilitiesCurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations