Collaborative Arrangements - Schedule of Collaborative Arrangement Transactions (Details) - Collaborative Arrangement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AstraZeneca \| Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	$ 52	$ 12
AstraZeneca \| Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	405	543
AstraZeneca \| Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	250	100
AstraZeneca \| Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total sales	187	20
AstraZeneca \| Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	93	4
AstraZeneca \| Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	48	1
AstraZeneca \| Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	152	2,419
Eisai \| Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	71
Eisai \| Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	375
Eisai \| Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	543
Eisai \| Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total sales	149
Eisai \| Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	39
Eisai \| Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	13
Eisai \| Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	1,489
Bayer AG \| Other current assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Receivables from counterparty	32	33
Bayer AG \| Accrued and other current liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	0	350
Bayer AG \| Other noncurrent liabilities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payables to counterparty	375	0
Bayer AG \| Total sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales recorded by Merck	190	149	$ 88
Merck’s profit share of sales in marketing territories	139	151	81
Total sales	329	300	169
Bayer AG \| Cost of sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	216	99	133
Bayer AG \| Selling, general and administrative
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	35	27	26
Bayer AG \| Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses	$ 127	$ 101	$ 82