Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock [Member]	Retained earnings [Member]	Accumulated other comprehensive loss, net of tax [Member]	Treasury stock, at cost [Member]	Common shares outstanding [Member]
Balance, beginning of year at Dec. 31, 2016		$ 22,614	$ 32,196	$ (755)	$ (30,834)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Employee share-based compensation		118
Compensation amortization under share-based plans and other changes		104
Net income	$ 1,505		1,505
Dividends			(591)
Other comprehensive income (loss)	470			470
Treasury stock acquired — share repurchase authorization					(1,028)
Net shares acquired related to employee share-based compensation plans					(61)
Balance, end of period at Sep. 30, 2017	23,738	22,836	33,110	(285)	(31,923)
Balance, beginning of year (in shares) at Dec. 31, 2016						279.6
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(8.3)
Net shares issued under employee share-based compensation plans (in shares)						2.4
Balance, end of period (in shares) at Sep. 30, 2017						273.7
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Cumulative effect of adoption of updated accounting guidance for equity financial instruments			22	(22)
Balance, beginning of year at Dec. 31, 2017	$ 23,731	22,886	33,462	(343)	(32,274)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Reclassification of certain tax effects from adoption of updated accounting guidance				(24)
Balance, beginning of year (in shares) at Dec. 31, 2017	271.4					271.4
Balance, beginning of year at Dec. 31, 2017	$ 23,731	22,886	33,462	(343)	(32,274)
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Employee share-based compensation		93
Compensation amortization under share-based plans and other changes		110
Reclassification of certain tax effects from adoption of updated accounting guidance			24	(24)
Net income	1,902		1,902
Dividends			(613)
Other			2
Other comprehensive income (loss)	(1,614)			(1,614)
Treasury stock acquired — share repurchase authorization	(1,100)				(1,100)
Net shares acquired related to employee share-based compensation plans	(51)				(51)
Balance, end of period at Sep. 30, 2018	$ 22,460	$ 23,089	$ 34,799	(2,003)	$ (33,425)
Balance, beginning of year (in shares) at Dec. 31, 2017	271.4					271.4
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)	(8.2)					(8.2)
Net shares issued under employee share-based compensation plans (in shares)						1.6
Balance, end of period (in shares) at Sep. 30, 2018	264.8					264.8
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Cumulative effect of adoption of updated accounting guidance for equity financial instruments				$ (22)