Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effect of Fourth Quarter Events [Line Items]
Product sales									$ 23,362	$ 23,747	$ 22,849
Gross profit from product sales	$ 4,628	$ 4,427	$ 4,562	$ 4,231	$ 4,905	$ 4,473	$ 4,655	$ 4,399
Net income	$ 1,703	$ 1,968	$ 2,179	$ 1,992	$ 1,928	$ 1,859	$ 2,296	$ 2,311	$ 7,842	$ 8,394	$ 1,979
Earnings per share:
Basic (in usd per share)	$ 2.87	$ 3.29	$ 3.59	$ 3.20	$ 3.04	$ 2.88	$ 3.50	$ 3.27	$ 12.96	$ 12.70	$ 2.71
Diluted (in usd per share)	$ 2.85	$ 3.27	$ 3.57	$ 3.18	$ 3.01	$ 2.86	$ 3.48	$ 3.25	$ 12.88	$ 12.62	$ 2.69
Product [Member]
Effect of Fourth Quarter Events [Line Items]
Product sales	$ 5,881	$ 5,463	$ 5,574	$ 5,286	$ 6,001	$ 5,510	$ 5,679	$ 5,343	$ 22,204	$ 22,533	$ 21,795