Leases Lease Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Operating	$ 70.9	$ 158.4
Total leased assets	76.6	167.1
Liabilities, Current
Operating	24.6	45.4
Liabilities, Noncurrent
Operating	45.4	85.7
Total lease liabilities	77.5	139.8
Operating lease right-of-use assets [Member]
Assets
Operating	70.9	158.4
Property and equipment (including concession assets), net [Member]
Assets
Finance	5.7	8.7
Accounts payable and accrued liabilities [Member]
Liabilities, Current
Operating	24.6	45.4
Long-term debt due within one year [Member]
Liabilities, Current
Finance	2.3	1.9
Long-term operating lease liabilities [Member]
Liabilities, Noncurrent
Operating	45.4	85.7
Long-term debt [Member]
Liabilities, Noncurrent
Finance	$ 5.2	$ 6.8