Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets
Pension liabilities	$ 76.4	$ 74.2
Retirement benefits other than pensions	79.4	77.8
Workers’ compensation and other claims	41.2	42.4
Property and equipment, net	2.5	4.1
Other assets and liabilities	120.6	135.2
Net operating loss carryforwards	37.1	47.4
Alternative minimum and other tax credits(a)	47.5	46.7
Subtotal	404.7	427.8
Valuation allowances	(45.7)	(40.1)	$ (32.4)	$ (47.4)
Total deferred tax assets	359.0	387.7
Deferred tax liabilities
Retirement benefits other than pensions	1.0	0.0
Other assets and miscellaneous	36.3	38.9
Deferred tax liabilities	37.3	38.9
Net deferred tax asset	321.7	348.8
Deferred Tax Assets (Liabilities), Net [Abstract]
Current assets	0.0	71.9
Noncurrent assets	329.8	289.5
Current liabilities	0.0	(1.8)
Noncurrent liabilities	(8.1)	(10.8)
Net deferred tax asset	321.7	$ 348.8
Operating Loss Carryforwards [Line Items]
Alternative minimum and other tax credits - unlimited carryforward period	32.5
U.S. foreign tax credits	12.3
Remaining credits	2.7
Foreign
Deferred tax assets
Net operating loss carryforwards	$ 24.4
Operating Loss Carryforwards [Line Items]
Carryforward period (in years)	10 years
Valuation allowance	$ 10.4