Principal Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Principal Accounting Policies [Line Items]
Reporting segments	4
Unearned revenue	$ 16.6	$ 13.6
Deferred costs	15.7	13.4
Cash-equivalent investments	398.5	388.1
Variable-rate demand notes	13.3
Long-term marketable securities	5.4	6.0
Depreciation expense	191.4	178.9	175.1
Amortization expense related to capitalized software	7.9	10.3	12.9
Accumulated amortization expense related to capitalized software	148.4	140.7
Book overdrafts	38.5	24.2
Liability related to assumed claims	57.7	49.8
Receivable from the re-insurance pool	44.0	44.7
Operating income from reinsurance pool	4.4	4.1	4.0
Marketing expenses	$ 4.2	$ 9.6	$ 9.7
Buildings [Member]
Principal Accounting Policies [Line Items]
Property, plant and equipment, estimated useful lives, years	25
Revenue Equipment [Member]
Principal Accounting Policies [Line Items]
Property, plant and equipment, minimum useful lives, years	4
Property, plant and equipment, maximum useful lives, years	14
Other Equipment [Member]
Principal Accounting Policies [Line Items]
Property, plant and equipment, minimum useful lives, years	3
Property, plant and equipment, maximum useful lives, years	10
Software [Member]
Principal Accounting Policies [Line Items]
Property, plant and equipment, minimum useful lives, years	3
Property, plant and equipment, maximum useful lives, years	7