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Collaborative Arrangements - Schedule of Transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sales	$ 12,080	$ 12,057
Cost of sales	3,670	3,312
Selling, general and administrative	2,633	2,555
Research and development	2,465	2,209
Payables, current	26,361		$ 27,327
Other current assets | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from Bayer included in Other current assets	236		215
Other current assets | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from Bayer included in Other current assets	153		157
Other current assets | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Receivables from Bayer included in Other current assets	68		65
Accounts payable and accrued liabilities | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables, current	417		423
Accounts payable and accrued liabilities | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables, current	300		335
Other Noncurrent Liabilities | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to Bayer included in Other Noncurrent Liabilities	300		600
Other Noncurrent Liabilities | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payables to Bayer included in Other Noncurrent Liabilities	400		$ 0
Revenue | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Alliance revenue - profit sharing	233	145
Revenue | AstraZeneca | Collaborative Arrangement | Alliance revenue - Lynparza (1)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Alliance revenue - profit sharing	228	145
Revenue | AstraZeneca | Collaborative Arrangement | Alliance revenue - Koselugo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Alliance revenue - profit sharing	5	0
Revenue | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Alliance revenue - profit sharing	130	128
Revenue | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Alliance revenue - profit sharing	74	53
Collaborative Arrangement, Sales, Net	55	56
Sales	129	109
Cost of sales | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of sales	42	28
Cost of sales | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of sales	47	35
Cost of sales | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of sales	189	28
Amortization of intangible assets	153
Selling, general and administrative | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Selling, general and administrative	40	33
Selling, general and administrative | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Selling, general and administrative	23	11
Selling, general and administrative | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Selling, general and administrative	32	15
Research and development | AstraZeneca | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development	29	36
Research and development | Eisai | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development	64	64
Research and development | Bayer AG | Collaborative Arrangement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development	$ 7	$ 25

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