Segment Information (Tables)

12 Months Ended

Dec. 31, 2013

Segment Reporting [Abstract]

Revenue by product

	For the Years Ended December 31,
	2013						2012						2011
(In millions)	United States		Rest of World		Total		United States		Rest of World		Total		United States		Rest of World		Total
AVONEX	$	1,902.4	$	1,103.1	$	3,005.5	$	1,793.7	$	1,119.4	$	2,913.1	$	1,628.3	$	1,058.3	$	2,686.6
TYSABRI	814.2		712.3		1,526.5		383.1		752.8		1,135.9		326.5		753.0		1,079.5
TECFIDERA	864.4		11.7		876.1		—		—		—		—		—		—
Other	—		134.2		134.2		—		117.1		117.1		—		70.0		70.0
Total product revenues	$	3,581.0	$	1,961.3	$	5,542.3	$	2,176.8	$	1,989.3	$	4,166.1	$	1,954.8	$	1,881.3	$	3,836.1

Geographic information

December 31, 2013 (In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenues from external customers	$	3,581.0	$	1,170.2	$	417.7	$	93.2	$	280.2	$	5,542.3
Revenues from unconsolidated joint business	$	1,087.3	$	1.6	$	—	$	3.2	$	33.9	$	1,126.0
Other revenues from external customers	$	193.5	$	26.1	$	1.2	$	43.1	$	—	$	263.9
Long-lived assets	$	984.4	$	758.3	$	2.5	$	2.1	$	3.3	$	1,750.7
December 31, 2012 (In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenues from external customers	$	2,176.8	$	1,216.2	$	409.2	$	93.2	$	270.7	$	4,166.1
Revenues from unconsolidated joint business	$	1,033.3	$	14.3	$	—	$	27.5	$	62.8	$	1,137.9
Other revenues from external customers	$	170.2	$	27.9	$	1.1	$	13.3	$	—	$	212.5
Long-lived assets	$	996.6	$	738.6	$	1.9	$	2.9	$	2.2	$	1,742.2
December 31, 2011 (In millions)	U.S.		Europe(1)		Germany		Asia		Other		Total
Product revenues from external customers	$	1,954.8	$	1,163.3	$	377.5	$	88.7	$	251.8	$	3,836.1
Revenues from unconsolidated joint business	$	878.8	$	29.9	$	—	$	30.7	$	57.2	$	996.6
Other revenues from external customers	$	187.0	$	28.3	$	0.6	$	—	$	—	$	215.9
Long-lived assets	$	1,012.5	$	816.6	$	1.6	$	5.3	$	2.4	$	1,838.4