Property and Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property and Equipment [Abstract]
Property, software and equipment depreciation, amortization expense	$ 150.8	$ 126.6	$ 105.8
Impairment of long-lived assets held-for-use	61.7	14.9
Long lived asset depreciation and amortization	59.9	14.5
Payroll and consulting fees for software	42.6	32.8	27.2
Non-cash stock based compensation	7.5	7.8	6.3
Write-off of internal use software costs	4.6	2.3
Internal-use software write-offs, accumulated depreciation	$ 3.9	$ 2.3