Profit Per Share (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended			2 Months Ended	3 Months Ended					9 Months Ended
		Oct. 31, 2018	Aug. 31, 2018	May 31, 2018	Jun. 30, 2018	Oct. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jul. 01, 2018	Jan. 31, 2014
Accelerated Stock Repurchase Agreement [Line Items]
Common shares repurchased (in shares)			4,800,000	1,600,000	3,300,000			3,100,000			12,804,035	0
Common shares under SARs and stock options not included in the computation of diluted earnings per share (in shares)							1,471,071		5,136,715
Share-based Compensation, Stock Options, Activity [Table Text Block]											nine
Accelerated share repurchase, amount				$ 500
Profit for the period (A) (in dollars)	[1]						$ 1,727		$ 1,059		$ 5,099	$ 2,053
Determination of shares (in millions)
Weighted-average number of common shares outstanding (B) (in shares)							592,100,000		592,900,000		595,300,000	590,300,000
Shares issuable on exercise of stock awards, net of shares assumed to be purchased out of proceeds at average market price (in shares)							7,300,000		7,200,000		8,500,000	6,200,000
Average common shares outstanding for fully diluted computation (C) (in shares)	[2]						599,400,000		600,100,000		603,800,000	596,500,000
Profit (loss) per share of common stock:
Assuming no dilution (A/B) (in dollars per share)							$ 2.92		$ 1.79		$ 8.57	$ 3.48
Assuming full dilution (A/C) (in dollars per share)	[2]						$ 2.88		$ 1.77		$ 8.45	$ 3.44
Shares outstanding as of September 30 (in shares)							590,100,000		594,900,000		590,100,000	594,900,000
Common stock repurchase
Stock repurchase program, authorized amount							$ 750				$ 750		$ 10,000	$ 10,000
Common shares repurchased (in shares)			4,800,000	1,600,000	3,300,000			3,100,000			12,804,035	0
Payments for repurchase of common stock			$ 750	$ 250				$ 500		$ 750	$ 2,000	$ 0
Stock repurchase program, remaining authorized repurchase amount							$ 3,500				$ 3,500
Subsequent Event [Member]
Accelerated Stock Repurchase Agreement [Line Items]
Common shares repurchased (in shares)		400,000				5,200,000
Common stock repurchase
Common shares repurchased (in shares)		400,000				5,200,000

[1] 1 Profit attributable to common shareholders.

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