Commitments and Contingencies - Additional Information (Details)	1 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2020 USD ($) plaintiff	Dec. 31, 2018 USD ($)	Apr. 30, 2020
Loss Contingencies [Line Items]
Number of plaintiffs involved | plaintiff			19,000
Indenix
Loss Contingencies [Line Items]
Damages awarded		$ 2,540,000,000
Past damages vacated				$ 2,540,000,000
Juno
Loss Contingencies [Line Items]
Damages awarded	$ 585,000,000
Running royalty rate from October 2017	27.60%
Enhancement rate on past damages					50.00%
Running royalty rate on future sales					27.60%
Estimate of possible loss representing past sales			$ 811,000,000
Estimate of possible loss representing enhancement of past damages			389,000,000
Estimate of possible loss representing royalties and prejudgment interest			128,000,000
Juno | Minimum
Loss Contingencies [Line Items]
Estimate of possible loss			0
Juno | Maximum
Loss Contingencies [Line Items]
Estimate of possible loss			$ 1,300,000,000