Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock [Member]	Retained earnings [Member]	Accumulated other comprehensive income (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		68
Compensation amortization under share-based plans		42
Net income	$ 617		617
Dividends			(190)
Other comprehensive income (loss)	140			140
Treasury stock acquired — share repurchase authorization					(225)
Net shares acquired related to employee share-based compensation plans					(61)
Balance, end of period at Mar. 31, 2017	23,612	22,724	32,623	(615)	(31,120)
Balance, beginning of year (in shares) at Dec. 31, 2016						279.6
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)						(1.9)
Net shares issued under employee share-based compensation plans (in shares)						1.7
Balance, end of period (in shares) at Mar. 31, 2017						279.4
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		65
Compensation amortization under share-based plans		44
Reclassification of certain tax effects from adoption of updated accounting guidance			24	(24)
Net income	669		669
Dividends			(197)
Other			1
Other comprehensive income (loss)	(933)			(933)
Treasury stock acquired — share repurchase authorization	(350)				(350)
Net shares acquired related to employee share-based compensation plans	(51)				(51)
Balance, end of period at Mar. 31, 2018	$ 22,979	$ 22,995	$ 33,981	$ (1,322)	$ (32,675)
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)	(2.5)					(2.5)
Net shares issued under employee share-based compensation plans (in shares)						1.3
Balance, end of period (in shares) at Mar. 31, 2018	270.2					270.2