Segment Reporting (Revenue by Product) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Product sales									$ 14,448.9	$ 10,885.8	$ 6,099.9
Royalties and other revenues									711.7	510.8	316.8
Total revenues	$ 4,144.9	$ 3,697.6	$ 3,745.8	$ 3,572.3	$ 3,806.1	$ 3,452.1	$ 2,429.1	$ 1,709.3	15,160.6	11,396.6	6,416.7
Immunology
Revenue from External Customer [Line Items]
Product sales									4,370.3	2,827.0	1,062.7
IMMUNOGLOBULIN THERAPIES
Revenue from External Customer [Line Items]
Product sales									2,236.6	1,143.9	0.0
HEREDITARY ANGIOEDEMA
Revenue from External Customer [Line Items]
Product sales									1,429.6	1,310.9	1,062.7
BIO THERAPEUTICS
Revenue from External Customer [Line Items]
Product sales									704.1	372.2	0.0
Hematology
Revenue from External Customer [Line Items]
Product sales									3,785.6	2,240.8	0.0
HEMOPHILIA
Revenue from External Customer [Line Items]
Product sales									2,957.3	1,789.0	0.0
INHIBITOR THERAPIES
Revenue from External Customer [Line Items]
Product sales									828.3	451.8	0.0
Neuroscience
Revenue from External Customer [Line Items]
Product sales									2,664.1	2,490.5	2,200.4
VYVANSE
Revenue from External Customer [Line Items]
Product sales									2,161.1	2,013.9	1,722.2
ADDERALL XR
Revenue from External Customer [Line Items]
Product sales									348.0	363.8	362.8
MYDAYIS
Revenue from External Customer [Line Items]
Product sales									21.6	0.0	0.0
Other Neuroscience
Revenue from External Customer [Line Items]
Product sales									133.4	112.8	115.4
Internal Medicine
Revenue from External Customer [Line Items]
Product sales									1,670.3	1,755.5	1,500.6
LIALDA/MEZAVANT
Revenue from External Customer [Line Items]
Product sales									569.4	792.1	684.4
GATTEX/REVESTIVE
Revenue from External Customer [Line Items]
Product sales									335.5	219.4	141.7
PENTASA
Revenue from External Customer [Line Items]
Product sales									313.2	309.4	305.8
NATPARA/NATPAR
Revenue from External Customer [Line Items]
Product sales									147.4	85.3	24.4
Other Internal Medicine
Revenue from External Customer [Line Items]
Product sales									304.8	349.3	344.3
Genetic Diseases
Revenue from External Customer [Line Items]
Product sales									1,437.7	1,387.1	1,336.2
ELAPRASE
Revenue from External Customer [Line Items]
Product sales									615.7	589.0	552.6
REPLAGAL
Revenue from External Customer [Line Items]
Product sales									472.1	452.4	441.2
VPRIV
Revenue from External Customer [Line Items]
Product sales									349.9	345.7	342.4
Oncology
Revenue from External Customer [Line Items]
Product sales									261.7	130.5	0.0
Ophthalmics
Revenue from External Customer [Line Items]
Product sales									259.2	54.4	0.0
Royalties
Revenue from External Customer [Line Items]
Royalties and other revenues									448.4	382.6	300.5
Other revenues
Revenue from External Customer [Line Items]
Royalties and other revenues									$ 263.3	$ 128.2	$ 16.3