Other Investments (Details) - USD ($) $ in Millions		1 Months Ended							3 Months Ended			6 Months Ended		12 Months Ended
	Dec. 09, 2019	Apr. 30, 2020	Mar. 31, 2020	Oct. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Other Investments												$ 38.1	$ 43.8
Other income and (expense)									$ 0.2		$ 0.1	(0.7)	2.5
Unrealized gain on strategic equity investments												(25.8)	(8.6)
Zealand
Schedule of Equity Method Investments [Line Items]
Unrealized gain on strategic equity investments									0.8		(2.9)	1.0	(3.6)
Equity Securities, FV-NI									27.5	$ 28.5		27.5		$ 28.5
Payments to Acquire Equity Method Investments						$ 13.8
Moderna LLC
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Other Investments															$ 37.5
Unrealized gain on strategic equity investments											29.0		(0.8)
Proceeds from Sale of Equity Method Investments	$ 114.7
Equity Method Investment, Realized Gain (Loss) on Disposal	$ 77.2
Dicerna
Schedule of Equity Method Investments [Line Items]
Unrealized gain on strategic equity investments									(5.9)		(0.9)	(2.8)	(4.2)
Equity Securities, FV-NI									21.2	18.4		21.2		18.4
Payments to Acquire Equity Method Investments								$ 10.3
Caelum
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Other Investments							$ 41.0					41.0		64.0
Option To Acquire Remaining Equity, Amount							$ 16.1
Other income and (expense)										32.0
Eidos
Schedule of Equity Method Investments [Line Items]
Unrealized gain on strategic equity investments									(0.6)			3.1
Equity Securities, FV-NI									24.7	27.8		24.7		27.8
Payments to Acquire Equity Method Investments					$ 19.9
Stealth
Schedule of Equity Method Investments [Line Items]
Unrealized gain on strategic equity investments									(0.9)			1.9
Equity Securities, FV-NI									2.5	4.4		2.5		$ 4.4
Payments to Acquire Equity Method Investments				$ 9.6
Common Stock
Schedule of Equity Method Investments [Line Items]
Equity Securities, FV-NI									47.7			47.7
Portola Pharmaceuticals
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Other Investments		$ 3.6	$ 14.5
Unrealized gain on strategic equity investments									(29.0)			(29.6)
Collaborative Arrangement | Caelum
Schedule of Equity Method Investments [Line Items]
Collaboration Agreement, Potential Future Payments										20.0
Research and development									$ 0.1		$ 0.3	$ 2.4	$ 0.3
Collaborative Agreement, Amendment | Caelum
Schedule of Equity Method Investments [Line Items]
Research and development										$ 4.1