Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Pension liabilities	$ 55.4	$ 56.2	$ 55.4
Retirement benefits other than pensions	73.8	71.8	73.8
Workers’ compensation and other claims	30.6	29.1	30.6
Property and equipment, net	7.1	5.2	7.1
Other assets and liabilities	88.5	88.6	88.5
Net operating loss carryforwards	42.0	41.1	42.0
Alternative minimum and other tax credits(a)	73.4	68.2	73.4
Subtotal	370.8	360.2	370.8
Valuation allowances	(100.7)	(98.9)	(100.7)	$ (62.8)	$ (45.7)
Total deferred tax assets	270.1	261.3	270.1
Deferred tax liabilities
Property and equipment, net	0.0	3.7	0.0
Goodwill and other intangibles	22.0	32.2	22.0
Other assets and miscellaneous	28.3	24.3	28.3
Deferred tax liabilities	50.3	60.2	50.3
Net deferred tax asset	219.8	201.1	219.8
Noncurrent assets	236.5	226.2	236.5
Noncurrent liabilities	(16.7)	(25.1)	(16.7)
Operating Loss Carryforwards [Line Items]
Tax Reform Act Tax Expense Charge		92.0
Foreign tax credit amount			69.6
Remaining credits	3.8		3.8
Foreign
Deferred tax assets
Net operating loss carryforwards	27.5		$ 27.5
Operating Loss Carryforwards [Line Items]
Carryforward period (in years)			10 years
Tax Cuts and Jobs Act of 2017
Operating Loss Carryforwards [Line Items]
Tax Reform Act Tax Expense Charge	2.0	92.0
Foreign tax credit amount	1.3	$ 31.1
State tax amount	$ 0.2