Accrued Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accrued Liabilities [Abstract]
Salaries, benefits and related expenses	$ 520.6	$ 470.0
Office and related expenses	57.9	62.0
Acquisition obligations	43.7	63.5
Interest	40.3	41.5
Professional fees	25.3	24.6
Other	139.3	118.9
Total accrued liabilities	$ 827.1	$ 780.5