Fair Value Measurements (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Fair value of contingent consideration obligations
Fair value, beginning of period	$ 151.0	$ 81.2
Additions	122.2	38.8
Changes in fair value	27.2	36.0
Payments	(6.5)	(5.0)
Fair value, end of period	$ 293.9	$ 151.0

Fair value, as of the acquisition date, of potential payments under the contingent consideration arrangement including cash and shares.

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+ Details