Income Taxes (Deferred tax liabilities and assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Depreciation	$ 109.0	$ 148.0
Deferred revenue	9.3	14.4
Intangibles	6.0	6.4
Gain on debt redemption	0.0	7.9
State taxes	19.9	22.1
Other	15.2	10.6
Deferred tax liabilities	159.4	209.4
Claims and insurance	(84.8)	(98.2)
Net operating loss carryforwards	(199.9)	(228.0)
Employee benefit accruals	(88.9)	(88.8)
Deferred Tax Asset, Sale Leaseback Transaction	(54.5)	(64.7)
Other	(20.6)	(31.7)
Deferred tax assets	(448.7)	(511.4)
Valuation allowance	291.1	305.1
Net deferred tax assets	(157.6)	(206.3)
Net deferred tax liability	$ 1.8	$ 3.1