Other Investments (Details) - USD ($) $ in Millions		1 Months Ended						3 Months Ended		9 Months Ended	12 Months Ended
	Dec. 09, 2019	Dec. 31, 2019	Oct. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Dec. 31, 2019	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2014
Payments to Acquire Other Investments											$ 73.3	$ 10.3	$ 0.0
Unrealized Gain (Loss) on Investments											26.9	40.2	0.0
Other income and (expense)											35.9	5.5	0.3
Research and Development Expense											886.0	730.4	$ 878.4
Moderna LLC [Member]
Payments to Acquire Other Investments														$ 37.5
Unrealized Gain (Loss) on Investments									$ 100.8		32.8	(56.4)
Payments to Acquire Other Investments												81.9
Proceeds from sale of investment	$ 114.7
Realized gain from sale of investment	$ 77.2
Dicerna [Member]
Unrealized Gain (Loss) on Investments											9.5	1.4
Payments to Acquire Equity Method Investments							$ 10.3
Equity Securities, FV-NI		$ 18.4						$ 18.4			18.4	$ 8.9
Caelum Biosciences [Member]
Payments to Acquire Other Investments											41.0
Option To Acquire Remaining Equity, Amount						$ 16.1					64.0
Other income and (expense)		32.0
Zealand [Member]
Unrealized Gain (Loss) on Investments										$ 14.7
Payments to Acquire Equity Method Investments					$ 13.8
Equity Securities, FV-NI		28.5						28.5			28.5
Eidos [Member] [Member]
Unrealized Gain (Loss) on Investments											7.9
Payments to Acquire Equity Method Investments				$ 19.9
Equity Securities, FV-NI		27.8						27.8			27.8
Stealth [Member]
Unrealized Gain (Loss) on Investments								(5.2)
Payments to Acquire Equity Method Investments			$ 9.6
Equity Securities, FV-NI		$ 4.4						$ 4.4			4.4
Collaborative Arrangement [Member] | Caelum Biosciences [Member]
Additional upfront funding accrued											20.0
Research and Development Expense											3.1
Collaborative Agreement, Amendment [Member] | Caelum Biosciences [Member]
Research and Development Expense											$ 4.1