Income Taxes - Components of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Depreciation	$ (83.8)	$ (99.5)
Operating lease right-of-use assets	(65.3)	(93.7)
Deferred revenue	(3.3)	(6.3)
Intangibles	(2.9)	(3.4)
State taxes	(19.6)	(19.6)
Other, including debt and interest	(22.3)	(16.0)
Deferred tax liabilities	(197.2)	(238.5)
Claims and insurance	84.4	89.9
Net operating loss carryforwards	216.7	210.7
Employee benefit accruals	23.9	94.8
Sale/leaseback transactions	53.0	55.5
Operating lease liabilities	68.7	93.8
Employer payroll taxes	20.0
Other, including debt and interest	37.0	28.4
Deferred tax assets	503.7	573.1
Valuation allowance	(305.6)	(334.0)
Net deferred tax assets	198.1	239.1
Net deferred tax asset	$ 0.9	$ 0.6