Segment Reporting (Revenue by Product) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenue from External Customer [Line Items]
Product sales	$ 3,533.8	$ 3,315.4	$ 10,537.9	$ 7,264.8
Royalties and other revenues	163.8	136.7	477.8	325.7
Total revenues	3,697.6	3,452.1	11,015.7	7,590.5
Hematology
Revenue from External Customer [Line Items]
Product sales	916.0	884.1	2,751.5	1,233.7
HEMOPHILIA
Revenue from External Customer [Line Items]
Product sales	725.3	702.4	2,119.6	978.0
INHIBITOR THERAPIES
Revenue from External Customer [Line Items]
Product sales	190.7	181.7	631.9	255.7
Immunology
Revenue from External Customer [Line Items]
Product sales	801.7	606.5	2,160.6	796.0
IMMUNOGLOBULIN THERAPIES
Revenue from External Customer [Line Items]
Product sales	605.1	472.5	1,613.9	610.7
BIO THERAPEUTICS
Revenue from External Customer [Line Items]
Product sales	196.6	134.0	546.7	185.3
Neuroscience
Revenue from External Customer [Line Items]
Product sales	691.1	616.5	1,979.8	1,901.8
VYVANSE
Revenue from External Customer [Line Items]
Product sales	538.4	512.6	1,620.3	1,539.5
ADDERALL XR
Revenue from External Customer [Line Items]
Product sales	106.0	80.5	242.3	281.1
MYDAYIS
Revenue from External Customer [Line Items]
Product sales	10.2	0.0	25.9	0.0
Other Neuroscience
Revenue from External Customer [Line Items]
Product sales	36.5	23.4	91.3	81.2
Genetic Diseases
Revenue from External Customer [Line Items]
Product sales	628.1	676.1	2,029.2	1,977.2
FIRAZYR
Revenue from External Customer [Line Items]
Product sales	195.5	146.3	461.4	411.3
ELAPRASE
Revenue from External Customer [Line Items]
Product sales	152.9	146.7	454.5	424.3
REPLAGAL
Revenue from External Customer [Line Items]
Product sales	117.2	118.9	349.0	340.5
VPRIV
Revenue from External Customer [Line Items]
Product sales	89.6	87.7	257.3	259.3
CINRYZE
Revenue from External Customer [Line Items]
Product sales	56.9	165.4	458.7	502.6
KALBITOR
Revenue from External Customer [Line Items]
Product sales	16.0	11.1	48.3	39.2
Internal Medicine
Revenue from External Customer [Line Items]
Product sales	351.0	462.7	1,254.1	1,266.3
LIALDA/MEZAVANT
Revenue from External Customer [Line Items]
Product sales	86.7	208.6	469.6	570.3
GATTEX/REVESTIVE
Revenue from External Customer [Line Items]
Product sales	84.9	58.1	229.2	154.3
PENTASA
Revenue from External Customer [Line Items]
Product sales	72.1	85.4	224.5	222.3
NATPARA
Revenue from External Customer [Line Items]
Product sales	39.1	23.3	103.3	58.8
Other Internal Medicine
Revenue from External Customer [Line Items]
Product sales	68.2	87.3	227.5	260.6
Oncology
Revenue from External Customer [Line Items]
Product sales	68.5	55.4	189.3	75.7
Ophthalmics
Revenue from External Customer [Line Items]
Product sales	77.4	14.1	173.4	14.1
SENSIPAR royalties
Revenue from External Customer [Line Items]
Royalties and other revenues	42.8	38.7	128.1	112.2
ADDERALL XR royalties
Revenue from External Customer [Line Items]
Royalties and other revenues	7.7	4.7	33.6	15.7
FOSRENOL royalties
Revenue from External Customer [Line Items]
Royalties and other revenues	14.3	13.7	35.0	34.3
3TC and ZEFFIX royalties
Revenue from External Customer [Line Items]
Royalties and other revenues	16.1	16.2	38.8	43.3
Other Royalties and revenues
Revenue from External Customer [Line Items]
Royalties and other revenues	$ 82.9	$ 63.4	$ 242.3	$ 120.2