Acquisition, Collaborations And Other Arrangements (Details) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended		6 Months Ended
	Jul. 17, 2020 USD ($) agreement	Jul. 13, 2020 USD ($) shares	Apr. 07, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 19, 2020 agreement	May 29, 2020 USD ($) shares
Acquisition, Collaborations and Other Arrangements [Line Items]
Acquired in-process research and development expenses				$ 4,524	$ 165	$ 4,621	$ 291
Stock-based compensation expense						309	317
Payments to acquire in process research and development						4,804	239
Arcus
Acquisition, Collaborations and Other Arrangements [Line Items]
Equity securities owned (in shares) | shares									2.2
Equity securities in offering									$ 61
Pionyr
Acquisition, Collaborations and Other Arrangements [Line Items]
Equity method investment, ownership percentage								49.90%
Number of agreements | agreement								2
Subsequent Event | Arcus
Acquisition, Collaborations and Other Arrangements [Line Items]
Equity securities owned (in shares) | shares		6.0
Equity securities in offering		$ 200
Payments to acquire in process research and development		$ 175
Equity method investment, ownership percentage		13.00%
Future maximum research and development payments		$ 400
Collaborative term		10 years
Future maximum milestone payments		$ 1,200
Purchase period		5 years
Maximum percentage of outstanding stock allowed to be purchased		35.00%
Restriction period		3 years
Subsequent Event | Tizona
Acquisition, Collaborations and Other Arrangements [Line Items]
Equity method investment, ownership percentage	49.90%
Number of agreements | agreement	2
Payments to acquire equity method investments	$ 300
Option fee and potential future milestone payments	$ 1,300
Merger and Option Agreements | Subsequent Event | Pionyr
Acquisition, Collaborations and Other Arrangements [Line Items]
Payments to acquire equity method investments		$ 275
Option exercise fee		315
Potential future maximum milestone payments		1,200
Research and Development Service Agreement | Subsequent Event | Pionyr
Acquisition, Collaborations and Other Arrangements [Line Items]
Initial R&D funding		80
Potential maximum future milestone payments		$ 115
Other Arrangements
Acquisition, Collaborations and Other Arrangements [Line Items]
Upfront collaboration expenses related to other collaborative arrangements				$ 25	165	$ 122	291
Cash payments made related to equity investments					$ 48		$ 104
Forty Seven
Acquisition, Collaborations and Other Arrangements [Line Items]
Share price (usd per share) | $ / shares			$ 95.50
Total consideration, net of acquired cash			$ 4,700
Acquired in-process research and development expenses			4,500
Assets acquired, net of cash			202
Stock-based compensation expense			$ 144