Profit per share (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		Jul. 01, 2018
Earnings Per Share [Abstract]
Profit for the period (A) (in millions of dollars)		$ 1,098	$ 1,494	$ 1,620	$ 1,881	$ 1,048	$ 1,727	$ 1,707	$ 1,665	$ 6,093	[1]	$ 6,147	[1]	$ 754	[1]
Determination of shares (in millions)
Weighted-average number of common shares outstanding (B) (in shares)										561,600,000		591,400,000		591,800,000
Shares issuable on exercise of stock awards, net of shares assumed to be purchased out of proceeds at average market price (in shares)										5,900,000		8,000,000.0		7,500,000
Average common shares outstanding for fully diluted computation (C) (in shares)	[2]									567,500,000		599,400,000		599,300,000
Profit (loss) per share of common stock:
Assuming no dilution (A/B) (in dollars per share)		$ 2.00	$ 2.69	$ 2.85	$ 3.29	$ 1.80	$ 2.92	$ 2.86	$ 2.78	$ 10.85		$ 10.39		$ 1.27
Assuming full dilution (A/C) (in dollars per share)		$ 1.97	$ 2.66	$ 2.83	$ 3.25	$ 1.78	$ 2.88	$ 2.82	$ 2.74	$ 10.74	[2]	$ 10.26	[2]	$ 1.26	[2]
Shares outstanding as of December 31		550,100,000				575,500,000				550,100,000		575,500,000		597,600,000
Common shares under SARs and stock options not included in the computation of diluted earnings per share (in shares)										3,000,000.0		1,500,000		0
Common Stock Repurchase
Stock Repurchase Program, Authorized Amount																$ 10,000
Common shares repurchased (in shares)										30,586,507		27,673,675		0
Payments for repurchase of common stock										$ 4,047		$ 3,798		$ 0

[1] Profit attributable to common shareholders.

[2] Diluted by assumed exercise of stock-based compensation awards, using the treasury stock method.