Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Assets [Abstract]
Pension liabilities	$ 74.2	$ 70.0
Retirement benefits other than pensions	77.8	60.7
Workers' compensation and other claims	42.4	35.1
Property and equipment, net	4.1	0
Other assets and liabilities	135.2	138.6
Net operating loss carryforwards	47.4	26.8
Alternative minimum and other tax credits	46.7	44.7
Subtotal	427.8	375.9
Valuation Allowance	(40.1)	(32.4)	(47.4)	(43.9)
Total Deferred Tax Asset	387.7	343.5
Deferred Tax Liabilities [Abstract]
Property and equipment, net	0	9.9
Other assets and miscellaneous	38.9	31.0
Deferred tax liabilities	38.9	40.9
Net deferred tax asset	348.8	302.6
Deferred Tax Assets (Liabilities), Net [Abstract]
Current assets	71.9	72.0
Noncurrent assets	289.5	251.7
Current liabilities, included in accrued liabilities	(1.8)	(3.1)
Deferred Tax Liabilities, Noncurrent	(10.8)	(18.0)
Net deferred tax asset	348.8	302.6
Alternative minimum and other tax credits - unlimited carryforward period	34.4
Alternative minimum and other tax credits - various carryforward periods	1.9
Foreign Tax Credit Carryforward Amount	$ 10.4