Income Taxes (Deferred tax liabilities and assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Depreciation	$ 229.5	$ 256.3
Deferred revenue	15.8	13.9
Intangibles	8.9	16.2
Gain on debt redemption	25.7	38.5
State taxes	30.2	32.0
Other	31.5	27.5
Deferred tax liabilities	341.6	384.4
Claims and insurance	(149.6)	(165.7)
Net operating loss carryforwards	(302.9)	(302.4)
Employee benefit accruals	(201.8)	(221.9)
Deferred Tax Asset, Sale Leaseback Transaction	(99.9)	(107.0)
Other	(46.0)	(54.4)
Deferred tax assets	(800.2)	(851.4)
Valuation allowance	461.7	470.5
Net deferred tax assets	(338.5)	(380.9)
Net deferred tax liability	$ 3.1	$ 3.5