Segment Reporting (Revenue by Segment and Product) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from External Customer [Line Items]
Product sales	$ 3,637.1	$ 3,412.3
Royalties and other revenues	128.6	160.0
Rare Disease
Revenue from External Customer [Line Items]
Product sales	2,718.9	2,472.3
Royalties and other revenues	109.4	131.0
Rare Disease | Immunology
Revenue from External Customer [Line Items]
Product sales	1,125.9	1,042.3
Rare Disease | IMMUNOGLOBULIN THERAPIES
Revenue from External Customer [Line Items]
Product sales	557.9	498.3
Rare Disease | HEREDITARY ANGIOEDEMA
Revenue from External Customer [Line Items]
Product sales	368.8	366.1
Rare Disease | BIO THERAPEUTICS
Revenue from External Customer [Line Items]
Product sales	199.2	177.9
Rare Disease | Hematology
Revenue from External Customer [Line Items]
Product sales	952.6	870.9
Rare Disease | HEMOPHILIA
Revenue from External Customer [Line Items]
Product sales	742.8	650.4
Rare Disease | INHIBITOR THERAPIES
Revenue from External Customer [Line Items]
Product sales	209.8	220.5
Rare Disease | Genetic Diseases
Revenue from External Customer [Line Items]
Product sales	332.5	330.1
Rare Disease | REPLAGAL
Revenue from External Customer [Line Items]
Product sales	124.2	109.7
Rare Disease | ELAPRASE
Revenue from External Customer [Line Items]
Product sales	118.4	140.6
Rare Disease | VPRIV
Revenue from External Customer [Line Items]
Product sales	89.9	79.8
Rare Disease | Internal Medicine
Revenue from External Customer [Line Items]
Product sales	178.9	132.1
Rare Disease | GATTEX/REVESTIVE
Revenue from External Customer [Line Items]
Product sales	96.2	69.0
Rare Disease | NATPARA/NATPAR
Revenue from External Customer [Line Items]
Product sales	45.0	29.7
Rare Disease | Other Internal Medicine
Revenue from External Customer [Line Items]
Product sales	37.7	33.4
Rare Disease | Oncology
Revenue from External Customer [Line Items]
Product sales	66.9	58.3
Rare Disease | Ophthalmics
Revenue from External Customer [Line Items]
Product sales	62.1	38.6
Rare Disease | United States
Revenue from External Customer [Line Items]
Product sales	1,597.1	1,468.4
Rare Disease | United States | Immunology
Revenue from External Customer [Line Items]
Product sales	836.5	814.8
Rare Disease | United States | IMMUNOGLOBULIN THERAPIES
Revenue from External Customer [Line Items]
Product sales	421.6	405.4
Rare Disease | United States | HEREDITARY ANGIOEDEMA
Revenue from External Customer [Line Items]
Product sales	332.4	339.7
Rare Disease | United States | BIO THERAPEUTICS
Revenue from External Customer [Line Items]
Product sales	82.5	69.7
Rare Disease | United States | Hematology
Revenue from External Customer [Line Items]
Product sales	453.7	412.2
Rare Disease | United States | HEMOPHILIA
Revenue from External Customer [Line Items]
Product sales	393.1	341.5
Rare Disease | United States | INHIBITOR THERAPIES
Revenue from External Customer [Line Items]
Product sales	60.6	70.7
Rare Disease | United States | Genetic Diseases
Revenue from External Customer [Line Items]
Product sales	77.7	73.7
Rare Disease | United States | REPLAGAL
Revenue from External Customer [Line Items]
Product sales	0.0	0.0
Rare Disease | United States | ELAPRASE
Revenue from External Customer [Line Items]
Product sales	41.0	38.2
Rare Disease | United States | VPRIV
Revenue from External Customer [Line Items]
Product sales	36.7	35.5
Rare Disease | United States | Internal Medicine
Revenue from External Customer [Line Items]
Product sales	124.2	86.8
Rare Disease | United States | GATTEX/REVESTIVE
Revenue from External Customer [Line Items]
Product sales	80.3	57.0
Rare Disease | United States | NATPARA/NATPAR
Revenue from External Customer [Line Items]
Product sales	43.2	29.6
Rare Disease | United States | Other Internal Medicine
Revenue from External Customer [Line Items]
Product sales	0.7	0.2
Rare Disease | United States | Oncology
Revenue from External Customer [Line Items]
Product sales	43.4	42.3
Rare Disease | United States | Ophthalmics
Revenue from External Customer [Line Items]
Product sales	61.6	38.6
Rare Disease | International
Revenue from External Customer [Line Items]
Product sales	1,121.8	1,003.9
Rare Disease | International | Immunology
Revenue from External Customer [Line Items]
Product sales	289.4	227.5
Rare Disease | International | IMMUNOGLOBULIN THERAPIES
Revenue from External Customer [Line Items]
Product sales	136.3	92.9
Rare Disease | International | HEREDITARY ANGIOEDEMA
Revenue from External Customer [Line Items]
Product sales	36.4	26.4
Rare Disease | International | BIO THERAPEUTICS
Revenue from External Customer [Line Items]
Product sales	116.7	108.2
Rare Disease | International | Hematology
Revenue from External Customer [Line Items]
Product sales	498.9	458.7
Rare Disease | International | HEMOPHILIA
Revenue from External Customer [Line Items]
Product sales	349.7	308.9
Rare Disease | International | INHIBITOR THERAPIES
Revenue from External Customer [Line Items]
Product sales	149.2	149.8
Rare Disease | International | Genetic Diseases
Revenue from External Customer [Line Items]
Product sales	254.8	256.4
Rare Disease | International | REPLAGAL
Revenue from External Customer [Line Items]
Product sales	124.2	109.7
Rare Disease | International | ELAPRASE
Revenue from External Customer [Line Items]
Product sales	77.4	102.4
Rare Disease | International | VPRIV
Revenue from External Customer [Line Items]
Product sales	53.2	44.3
Rare Disease | International | Internal Medicine
Revenue from External Customer [Line Items]
Product sales	54.7	45.3
Rare Disease | International | GATTEX/REVESTIVE
Revenue from External Customer [Line Items]
Product sales	15.9	12.0
Rare Disease | International | NATPARA/NATPAR
Revenue from External Customer [Line Items]
Product sales	1.8	0.1
Rare Disease | International | Other Internal Medicine
Revenue from External Customer [Line Items]
Product sales	37.0	33.2
Rare Disease | International | Oncology
Revenue from External Customer [Line Items]
Product sales	23.5	16.0
Rare Disease | International | Ophthalmics
Revenue from External Customer [Line Items]
Product sales	0.5	0.0
Neuroscience
Revenue from External Customer [Line Items]
Product sales	918.2	940.0
Royalties and other revenues	19.2	29.0
Neuroscience | VYVANSE
Revenue from External Customer [Line Items]
Product sales	628.8	563.7
Neuroscience | ADDERALL XR
Revenue from External Customer [Line Items]
Product sales	76.0	64.9
Neuroscience | PENTASA
Revenue from External Customer [Line Items]
Product sales	72.4	69.1
Neuroscience | LIALDA/MEZAVANT
Revenue from External Customer [Line Items]
Product sales	62.0	175.1
Neuroscience | MYDAYIS
Revenue from External Customer [Line Items]
Product sales	4.5	0.0
Neuroscience | Other Neuroscience
Revenue from External Customer [Line Items]
Product sales	74.5	67.2
Neuroscience | United States
Revenue from External Customer [Line Items]
Product sales	757.9	816.4
Neuroscience | United States | VYVANSE
Revenue from External Customer [Line Items]
Product sales	557.2	508.5
Neuroscience | United States | ADDERALL XR
Revenue from External Customer [Line Items]
Product sales	72.1	59.3
Neuroscience | United States | PENTASA
Revenue from External Customer [Line Items]
Product sales	72.4	69.1
Neuroscience | United States | LIALDA/MEZAVANT
Revenue from External Customer [Line Items]
Product sales	30.5	153.1
Neuroscience | United States | MYDAYIS
Revenue from External Customer [Line Items]
Product sales	4.5	0.0
Neuroscience | United States | Other Neuroscience
Revenue from External Customer [Line Items]
Product sales	21.2	26.4
Neuroscience | International
Revenue from External Customer [Line Items]
Product sales	160.3	123.6
Neuroscience | International | VYVANSE
Revenue from External Customer [Line Items]
Product sales	71.6	55.2
Neuroscience | International | ADDERALL XR
Revenue from External Customer [Line Items]
Product sales	3.9	5.6
Neuroscience | International | PENTASA
Revenue from External Customer [Line Items]
Product sales	0.0	0.0
Neuroscience | International | LIALDA/MEZAVANT
Revenue from External Customer [Line Items]
Product sales	31.5	22.0
Neuroscience | International | MYDAYIS
Revenue from External Customer [Line Items]
Product sales	0.0	0.0
Neuroscience | International | Other Neuroscience
Revenue from External Customer [Line Items]
Product sales	$ 53.3	$ 40.8