Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, IO Collaboration (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Increase as a result of payment received from Sanofi	$ 401.1	$ (84.2)
Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Increase as a result of payment received from Sanofi	415.9
Revenue recognized that was included in deferred revenue at the beginning of the period	(55.3)
Revenue recognized that was added to deferred revenue during the period	$ (25.0)

Contract With Customer, Liability, Revenue Recognized From Prior Period

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- Definition

Contract With Customer, Liability, Revenue Recognized In Current Period

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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