Right of use assets and lease liabilities (Details) $ in Millions	Sep. 30, 2019 USD ($)
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	$ 2.8
Operating Lease, Right-of-Use Asset	93.7
Finance Lease, Liability	2.8
Operating Lease, Liability	93.7
Property, Plant and Equipment, Net [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	2.8
Operating Lease, Right-of-Use Asset	0.0
Other Assets and Deferred Charges [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Right-of-Use Asset	0.0
Operating Lease, Right-of-Use Asset	93.7
Accrued expenses and other [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	0.9
Operating Lease, Liability	21.4
Postretirement benefits and other long-term liabilities [Member]
Right of use assets and lease liabilities [Line Items]
Finance Lease, Liability	1.9
Operating Lease, Liability	$ 72.3