Accrued Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 363.5	$ 478.2
Office and related expenses	48.4	51.6
Acquisition obligations	36.1	29.5
Interest	33.9	42.4
Professional fees	20.7	21.7
Other	93.8	104.8
Total accrued liabilities	$ 596.4	$ 728.2