Property and Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property and Equipment [Abstract]
Property, software and equipment depreciation, amortization expense	$ 183.2	$ 150.8	$ 126.6
Impairment of long-lived assets held-for-use	77.4	61.7
Long lived asset depreciation and amortization	76.1	59.9
Payroll and consulting fees for software	54.2	42.6	32.8
Non-cash stock based compensation	9.3	7.5	7.8
Write-off of internal use software costs	14.1	4.6
Internal-use software write-offs, accumulated depreciation	$ 14.0	$ 3.9