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		94
Compensation amortization under share-based plans		73
Net income	$ 1,212		1,212
Dividends			(391)
Other			(1)
Other comprehensive income (loss)	411			411
Treasury stock acquired — share repurchase authorization					(700)
Net shares acquired related to employee share-based compensation plans					(61)
Balance, end of period at Jun. 30, 2017	23,858	22,781	33,016	(344)	(31,595)
Balance, beginning of year (in shares) at Dec. 31, 2016						279.6
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(5.7)
Net shares issued under employee share-based compensation plans (in shares)						2.0
Balance, end of period (in shares) at Jun. 30, 2017						275.9
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
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]
Employee share-based compensation		77
Compensation amortization under share-based plans		77
Reclassification of certain tax effects from adoption of updated accounting guidance			24	(24)
Net income	1,193		1,193
Dividends			(406)
Other			1
Other comprehensive income (loss)	(1,299)			(1,299)
Treasury stock acquired — share repurchase authorization	(700)				(700)
Net shares acquired related to employee share-based compensation plans	(51)				(51)
Balance, end of period at Jun. 30, 2018	$ 22,623	$ 23,040	$ 34,296	(1,688)	$ (33,025)
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)	(5.2)					(5.2)
Net shares issued under employee share-based compensation plans (in shares)						1.5
Balance, end of period (in shares) at Jun. 30, 2018	267.7					267.7
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Cumulative effect of adoption of updated accounting guidance for equity financial instruments				$ (22)