Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred Tax Assets [Abstract]
Retirement benefits other than pensions	$ 127.2	$ 112.7
Pension liabilities	136.4	138.3
Workers' compensation and other claims	38.3	42.8
Other assets and liabilities	115.3	107.0
Net operating loss carryforwards	63.5	44.9
Alternative minimum and other tax credits	37.9	37.7
Subtotal	518.6	483.4
Valuation Allowance	(47.4)	(43.9)
Net Deferred Tax Asset	471.2	439.5
Deferred Tax Liabilities [Abstract]
Property and equipment, net	11.2	12.5
Other assets and miscellaneous	37.4	37.0
Deferred tax liabilities	48.6	49.5
Net deferred tax asset	422.6	390.0
Deferred Tax Assets (Liabilities), Net [Abstract]
Current assets	59.4	66.4
Noncurrent assets	385.3	350.8
Current liabilities, included in accrued liabilities	(3.4)	(4.2)
Deferred Tax Liabilities, Noncurrent	(18.7)	(23.0)
Net deferred tax asset	422.6	390.0
Alternative minimum and other tax credits - unlimited carryforward period	37.3
Alternative minimum and other tax credits - various carryforward periods	$ 0.6