Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 917,419	$ 689,507
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	225,880	174,569
Share-based compensation	67,387	60,467
Deferred income taxes	(118,047)	(43,831)
Other	(42,495)	(21,070)
Changes in operating assets and liabilities, net:
Accounts receivable	(185,688)	(10,758)
Inventories	(129,171)	(44,363)
Other changes in operating assets and liabilities, net	68,866	25,685
Net cash flows provided by operating activities	804,151	830,206
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	4,404,707	1,423,931
Purchases of marketable securities	(1,617,974)	(1,253,934)
Acquisition of TYSABRI rights	(3,262,719)	0
Acquisitions of business, net of cash acquired	0	(72,401)
Purchases of property, plant and equipment	(87,440)	(127,447)
Other	(6,874)	(22,647)
Net cash flows used in investing activities	(570,300)	(52,498)
Cash flows from financing activities:
Purchase of treasury stock	(41,023)	(909,951)
Proceeds from issuance of stock for share-based compensation arrangements	39,002	43,081
Repayments of borrowings under senior notes	(452,340)	0
Other	45,174	33,166
Net cash flows used in financing activities	(409,187)	(833,704)
Net decrease in cash and cash equivalents	(175,336)	(55,996)
Effect of exchange rate changes on cash and cash equivalents	(2,878)	(1,735)
Cash and cash equivalents, beginning of the period	570,721	514,542
Cash and cash equivalents, end of the period	$ 392,507	$ 456,811