Subsequent Events	3 Months Ended
Mar. 31, 2013
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events TYSABRI On April 2, 2013, we acquired full ownership and strategic, commercial and decision-making rights to TYSABRI from Elan Pharma International, Ltd (Elan), an affiliate of Elan Corporation, plc. Upon the closing of the transaction, the previous collaboration agreement between Elan and us, whereby worldwide TYSABRI profits were split 50/50, was terminated. For additional information related to this collaboration, please read Note 21, Collaborative and Other Relationships to our consolidated financial statements included within our 2012 Form 10-K. Upon the closing of the transaction, we made an upfront payment of $3.25 billion to Elan. The transaction was funded from our existing cash and reverse repurchase agreements and will be accounted for as an asset acquisition. The upfront payment will be capitalized in the second quarter of 2013 as an intangible asset within our condensed consolidated balance sheets as TYSABRI has reached technological feasibility and will be amortized over the asset estimated useful life using an economic consumption method. Following the closing of the transaction, we will reflect 100% of the revenues, cost of sales and operating expenses related to TYSABRI within our condensed consolidated statements of income. We will continue to share TYSABRI profits with Elan equally until April 30, 2013. Commencing May 1, 2013 and for the first twelve months thereafter, we will make future contingent payments to Elan of 12% of worldwide net sales of TYSABRI, and thereafter, 18% on annual worldwide net sales up to $2.0 billion and 25% on annual worldwide net sales that exceed $2.0 billion. In 2014, the $2.0 billion threshold will be pro-rated for the portion of 2014 remaining after the first 12 months expires. Our payments to Elan will be recognized as cost of sales within our condensed consolidated statements of income.

Subsequent Events

TYSABRI

On April 2, 2013, we acquired full ownership and strategic, commercial and decision-making rights to TYSABRI from Elan Pharma International, Ltd (Elan), an affiliate of Elan Corporation, plc. Upon the closing of the transaction, the previous collaboration agreement between Elan and us, whereby worldwide TYSABRI profits were split 50/50, was terminated. For additional information related to this collaboration, please read Note 21, Collaborative and Other Relationships to our consolidated financial statements included within our 2012 Form 10-K.

Upon the closing of the transaction, we made an upfront payment of $3.25 billion to Elan. The transaction was funded from our existing cash and reverse repurchase agreements and will be accounted for as an asset acquisition. The upfront payment will be capitalized in the second quarter of 2013 as an intangible asset within our condensed consolidated balance sheets as TYSABRI has reached technological feasibility and will be amortized over the asset estimated useful life using an economic consumption method.

Following the closing of the transaction, we will reflect 100% of the revenues, cost of sales and operating expenses related to TYSABRI within our condensed consolidated statements of income. We will continue to share TYSABRI profits with Elan equally until April 30, 2013. Commencing May 1, 2013 and for the first twelve months thereafter, we will make future contingent payments to Elan of 12% of worldwide net sales of TYSABRI, and thereafter, 18% on annual worldwide net sales up to $2.0 billion and 25% on annual worldwide net sales that exceed $2.0 billion. In 2014, the $2.0 billion threshold will be pro-rated for the portion of 2014 remaining after the first 12 months expires. Our payments to Elan will be recognized as cost of sales within our condensed consolidated statements of income.