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Quarterly Financial Data (Unaudited) (Details Textual) - USD ($) shares in Millions, $ in Millions	1 Months Ended		3 Months Ended												9 Months Ended	12 Months Ended
	May 31, 2018	Oct. 31, 2017	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2013	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Jun. 05, 2018
Schedule Of Development Milestone And Collaboration [Line Items]
Unrealized gain (loss) on strategic investments			$ 2.8	$ (4.6)	$ (174.2)	$ 376.1	$ (12.2)	$ 141.2	$ 5.4	$ (6.4)
GILTI			(1,381.6)				(544.6)									$ (1,381.6)	$ (544.6)
Loss (gain) on fair value remeasurement of contingent consideration			(2.6)	57.8	$ 20.0	$ (11.5)	(79.3)	87.9	(1.9)	5.6						63.7	12.3	$ (62.7)
Research and development																2,280.6	2,597.2	2,253.6
Acquired in-process research and development																0.0	112.5	120.0
Payments to Noncontrolling Interests																(4.3)	36.4	134.1
Loss on divestiture of Hillerød, Denmark manufacturing operations																55.3	0.0	0.0
Net income (loss) attributable to noncontrolling interests, net of tax																0.0	43.3	131.0
Income tax benefit (expense)																1,158.0	1,425.6	2,458.7
Samsung Bioepis
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development expense on 2018 Ionis Agreement			63.0
Research and development														$ 46.0
Upfront And Milestone Payments Made To Collaborative Partner			100.0
Bristol-Myers Squibb
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development												$ 300.0				144.0	97.0
iPerian
Schedule Of Development Milestone And Collaboration [Line Items]
Developmental Milestone Payment												60.0
Alkermes
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development											$ 50.0					53.5	68.7	80.3
Upfront And Milestone Payments Made To Collaborative Partner											28.0
Ionis Pharmaceuticals
Schedule Of Development Milestone And Collaboration [Line Items]
Research and development expense on 2018 Ionis Agreement			45.0						486.2
Research and development									324.1							30.0			$ 10.0
Premium on purchase of common stock																				$ 162.1
Investment in common stock, shares purchased																				11.5
Upfront And Milestone Payments Made To Collaborative Partner											25.0
Neurimmune
Schedule Of Development Milestone And Collaboration [Line Items]
Payments to Noncontrolling Interests	$ 50.0	$ 150.0
Additional reduction in royalty rate payable on commercial sales	5.00%
Reduction in royalty rate payable on commercial sales		15.00%
TECFIDERA
Schedule Of Development Milestone And Collaboration [Line Items]
Impairment of in-licensed patent							176.8						$ 328.2
Karyopharm
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development										$ 10.0
Remedy Pharmaceutical
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development												$ 120.0
Pfizer
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development									$ 75.0
AliveGen
Schedule Of Development Milestone And Collaboration [Line Items]
Acquired in-process research and development								27.5
In-process research and development
Schedule Of Development Milestone And Collaboration [Line Items]
Impairment of IPR&D				$ 215.9				$ 189.3
2017 Tax Act
Schedule Of Development Milestone And Collaboration [Line Items]
GILTI							$ 135.8										$ 135.8
Income tax benefit (expense)																		1,200.0
Transition toll tax liabilities			697.0								$ 989.6					697.0		$ 989.6
Denmark Manufacturing Operations
Schedule Of Development Milestone And Collaboration [Line Items]
Loss on divestiture of Hillerød, Denmark manufacturing operations, net of tax			$ 40.2												$ 164.4	124.2
Loss on divestiture of Hillerød, Denmark manufacturing operations															$ 95.5	55.3
Tax expense on disposal group																$ 68.9