Leases - Aggregate lease maturities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Finance Leases
First year	$ 10.9	$ 15.5
Second year	7.7	11.8
Third year	3.8	5.8
Fourth year	0.7	1.3
Fifth year	0.3	0.4
Total lease payments, Finance leases	23.4	34.8
Less: Interest	1.1	1.9
Present value of lease liabilities	22.3	32.9
Operating Leases
First year	6.0	7.1
Second year	5.0	6.4
Third year	4.0	4.9
Fourth year	2.7	3.9
Fifth year	1.8	2.6
Thereafter	2.1	3.9
Total lease payments, Operating leases	21.6	28.8
Less: Interest	2.7	4.0
Present value of lease liabilities	$ 18.9	$ 24.8
Operating Lease, Liability, Statement of Financial Position	Current portion of long-term lease liability-operating, Long-term lease liability-operating	Current portion of long-term lease liability-operating, Long-term lease liability-operating
Total Finance and Operating Leases
First year	$ 16.9	$ 22.6
Second year	12.7	18.2
Third year	7.8	10.7
Fourth year	3.4	5.2
Fifth year	2.1	3.0
Thereafter	2.1	3.9
Total lease payments	45.0	63.6
Less: Interest	3.8	5.9
Present value of lease liabilities	$ 41.2	$ 57.7
Finance Lease, Liability, Statement of Financial Position	Long-term debt and finance lease obligations, net of debt issuance costs -less current portion, Current portion of long-term debt and finance lease obligations	Long-term debt and finance lease obligations, net of debt issuance costs -less current portion, Current portion of long-term debt and finance lease obligations