Income Taxes - Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred Tax Assets [Abstract]
Retirement benefits other than pensions	$ 112.7	$ 82.0
Pension liabilities	138.3	91.2
Workers' compensation and other claims	42.8	33.2
Property and equipment, net	0.2	0.4
Other assets and liabilities	106.8	99.7
Net operating loss carryforwards	44.9	38.6
Alternative minimum and other tax credits	37.7	46.8
Subtotal	483.4	391.9
Valuation Allowance	(43.9)	(45.9)
Net Deferred Tax Asset	439.5	346.0
Deferred Tax Liabilities [Abstract]
Property and equipment, net	12.5	10.6
Other assets and miscellaneous	37.0	45.8
Deferred tax liabilities	49.5	56.4
Net deferred tax asset	390.0	289.6
Deferred Tax Assets (Liabilities), Net [Abstract]
Current assets	66.4	48.3
Noncurrent assets	350.8	276.0
Current liabilities, included in accrued liabilities	(4.2)	(4.1)
Deferred Tax Liabilities, Noncurrent	(23.0)	(30.6)
Net deferred tax asset	390.0	289.6
Alternative minimum and other tax credits - unlimited carryforward period	36.8
Alternative minimum and other tax credits - various carryforward periods	$ 0.9