Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended						3 Months Ended					9 Months Ended	12 Months Ended
	Oct. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Nov. 30, 2018	Oct. 31, 2018	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2019
Commitments and Contingencies [Line Items]
Research and Development Expense													$ 886.0	$ 730.4	$ 878.4
Asset Acquisition, Contingent Consideration, Milestone Payments								$ 100.0
Other Commitment, potential payment							$ 60.6						60.6
Lonza Agreement [Member]
Commitments and Contingencies [Line Items]
Remaining total commitments with Lonza							1,099.9						1,099.9
CANADA
Commitments and Contingencies [Line Items]
Increase (Decrease) In Revenue From Contract With Customer, Excluding Assessed Tax													(29.8)
DOJ And OIG
Commitments and Contingencies [Line Items]
Loss Contingency Accrual, Payments													13.1
Canadian Patented Medicine Prices Review Board
Commitments and Contingencies [Line Items]
Escrow Deposit							43.4						43.4
Lonza Group AG [Member]
Commitments and Contingencies [Line Items]
Unrecorded Unconditional Purchase Obligation, Undiscounted Fixed Payment Amount							100.0						100.0
Collaborative Arrangement [Member] | Caelum Biosciences [Member]
Commitments and Contingencies [Line Items]
Collaboration Agreement, Upfront Payment				$ 30.0
Derivative Liability							24.0						24.0			$ 27.1
Additional upfront funding accrued													20.0
Additional equity interest funding													60.0
Collaboration Agreement, Potential Future Payments, Acquisition Option Exercise				500.0
Research and Development Expense													3.1
Collaboration Agreement, Potential Future Payments, Milestone Achievement				30.0
Zealand Pharma [Member] | Zealand [Member]
Commitments and Contingencies [Line Items]
Collaboration Agreement, Potential Future Payments, Option Fee												$ 15.0
Payments To Acquire Licenses And Equity Investment			$ 40.0
Prepaid Research And Development Expense		$ 5.0						5.0				5.0
Research and Development Expense									$ 21.2
Collaboration Agreement, Potential Future Payments, Milestone Achievement												610.0
Collaboration Agreement, Potential Future Payments, Additional Milestone Achievement												115.0
Collaboration and License Agreement [Member]
Commitments and Contingencies [Line Items]
Collaboration Agreement, Potential Future Payments, Milestone Achievement													54.0
Affibody AB [Member] | Affibody [Member]
Commitments and Contingencies [Line Items]
Payments To Acquire Licenses And Equity Investment			25.0
Collaboration Agreement, Potential Future Payments, Milestone Achievement												$ 625.0
Eidos [Member] [Member] | Eidos [Member] [Member]
Commitments and Contingencies [Line Items]
Payments To Acquire Licenses And Equity Investment		50.0
Research and Development Expense								$ 30.1
Collaboration Agreement, Potential Future Payments, Milestone Achievement													30.0
Dicerna Pharmaceutical Collaboration Agreement [Member] | Dicerna [Member]
Commitments and Contingencies [Line Items]
Payments To Acquire Licenses And Equity Investment						$ 37.0
Research and Development Expense							20.0			$ 26.7
Research and Development Arrangement, Potential Payment, Maximum							629.1						629.1
License Agreement 1 [Member] | Halozyme Therapeutics, Inc [Member]
Commitments and Contingencies [Line Items]
Research and Development Arrangement, Potential Payment, Maximum							160.0						$ 160.0
Research and Development Expense (Excluding Acquired in Process Cost)											$ 40.0
Caelum Biosciences [Member] | Collaborative Arrangement [Member]
Commitments and Contingencies [Line Items]
Equity Method Investment, Aggregate Cost				$ 57.1
Zealand [Member]
Commitments and Contingencies [Line Items]
Payments to Acquire Equity Method Investments			$ 13.8
Eidos [Member] [Member]
Commitments and Contingencies [Line Items]
Payments to Acquire Equity Method Investments		$ 19.9
Stealth [Member]
Commitments and Contingencies [Line Items]
Payments To Acquire Licenses And Equity Investment	$ 30.0
Payments to Acquire Equity Method Investments	$ 9.6
Stealth [Member] | Option Agreement [Member]
Commitments and Contingencies [Line Items]
Research and Development Expense							$ 20.4
Dicerna [Member]
Commitments and Contingencies [Line Items]
Payments to Acquire Equity Method Investments						$ 10.3
Syntimmune, Inc [Member]
Commitments and Contingencies [Line Items]
Asset Acquisition, Contingent Consideration, Milestone Payments					$ 800.0