Leasing - Assets and liabilities, lessee (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets
Operating lease assets	$ 146.2	$ 157.3
Finance lease assets	80.6	69.5
Total lease assets	226.8	226.8
Current liabilities:
Current portion of operating lease liabilities	42.8	47.4
Current portion of finance lease liabilities	23.6	20.9
Noncurrent liabilities:
Operating lease liabilities	111.4	114.5
Finance lease liabilities	59.2	50.3
Total lease liabilities	$ 237.0	$ 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