Subsequent Event - Narrative (Details) - Subsequent Event - Provisional Collaborative Arrangement $ / shares in Units, shares in Millions, $ in Millions	Aug. 05, 2020 USD ($) program $ / shares shares
Subsequent Event [Line Items]
Funded percentage	40.00%
U.S.
Subsequent Event [Line Items]
Agreed share of commercial profit (loss) percentage	50.00%
China
Subsequent Event [Line Items]
Agreed share of commercial profit (loss) percentage	40.00%
Biogen
Subsequent Event [Line Items]
Funded percentage	60.00%
Biogen \| U.S.
Subsequent Event [Line Items]
Agreed share of commercial profit (loss) percentage	50.00%
Biogen \| China
Subsequent Event [Line Items]
Agreed share of commercial profit (loss) percentage	60.00%
Biogen
Subsequent Event [Line Items]
Number of programs \| program	2
Number of additional programs, if circumstances met \| program	2
Upfront payment, to be received	$ 560
Eligible milestone payments, exceeding	1,100
Biogen \| Share Purchase Agreement
Subsequent Event [Line Items]
Proceeds to be received upon sale	$ 465
Number of common stock, to be issued (in shares) \| shares	13.3
Number of common stock, to be issued, per share (usd per share) \| $ / shares	$ 34.94
Outstanding share capital	11.20%

Aggregate Clinical Regulatory And Sales Milestone Payment

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- Definition

Collaborative Agreement, Agreed Share Of Commercial Profit (Loss)

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- Definition

Collaborative Agreement, Funded Percentage

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- Definition

Collaborative Arrangement, Number Of Additional Programs, If Circumstances Met

+ References

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- Definition

Collaborative Arrangement, Number Of Programs

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- Definition

Collaborative Arrangement, Upfront Payment, To Be Received

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- Definition

Sale Of Stock, Consideration To Be Received On Transaction

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- Definition

Sale Of Stock, Number Of Shares To Be Issued In Transaction

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- Definition

Sale Of Stock, Number Of Shares To Be Issued In Transaction, Price Per Share

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- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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