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Cost of Revenue (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
Cost of Revenue (Details) (USD $) In Millions	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Cost of Revenue (Textuals) [Abstract]
Corporate office costs	$ 47.8	$ 42.4	$ 89.5	$ 80.2
Stock-based compensation expenses	$ 10.8	$ 10.7	$ 20.7	$ 20.4

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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