Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accounting Policies [Abstract]
Accounts payable adjustment	$ 2,613.6	$ 2,332.2
Accrued liabilities adjustment	(2,613.6)	(2,332.2)
Revenue reclassification adjustment		(24.6)	(20.2)
Office and general expense reclassification adjustment		(24.6)	(20.2)
Furniture, equipment and computer software costs, useful life minimum	3
Furniture, equipment and computer software costs, useful life maximum	7
Buildings, useful life minimum	10
Buildings, useful life maximum	35
Leasehold improvements, useful life	the shorter of the useful life or the remaining lease term
Number of Reporting Units for Purposes of Annual Goodwill Impairment Test	11
Finite-Lived Intangible Assets, Useful Life, Minimum	7
Finite-Lived Intangible Assets, Useful Life, Maximum	15
Foreign currency transaction pre-tax loss	$ 0.9	$ 0.7	$ 4.7