Acquisitions (Narrative) (Details) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended
	May 25, 2018 USD ($)	Oct. 31, 2019 USD ($) $ / shares	Nov. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2018 kr / shares
Business Acquisition [Line Items]
Asset Acquisition, Contingent Consideration, Milestone Payments				$ 100.0
Syntimmune, Inc [Member]
Business Acquisition [Line Items]
Upfront payment for acquisition of Syntimmune outstanding shares			$ 400.0
Asset Acquisition, Contingent Consideration, Milestone Payments			800.0
Asset Acquisition, Potential Consideration Transfered, Including Contingent Consideration Milestone Payments			1,200.0
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, In-Process Research And Development			$ 375.2			$ 379.3
Achillion [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred		$ 926.0
Business Combination, Consideration Transferred, Per Share | $ / shares		$ 6.30
In Process Research and Development [Member]
Business Acquisition [Line Items]
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, Finite-Lived Intangibles	$ 803.7
Asset Acquisition, Share Price | kr / shares							kr 232
Asset Acquisition, Potential Payments For Development, Regulatory, Commercial Milestones And Royalties On Sales	19.0
Upfront payment for acquisition of Syntimmune outstanding shares	$ 749.3
In Process Research and Development [Member] | Syntimmune, Inc [Member]
Business Acquisition [Line Items]
Asset Acquisition, Recognized Benefit From Previously Acquired Research And Development					$ 4.1
Danicopan [Member] | Achillion [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Per Share | $ / shares		1.00
ACH-5528, Phase 3 [Member] | Achillion [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability, Per Share | $ / shares		$ 1.00