Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common stock [Member]	Retained earnings [Member]	Retained earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated other comprehensive income, net of tax [Member]	Treasury stock, at cost [Member]	Common shares outstanding [Member]
Shareholders' Equity [Roll Forward]
Shareholders' equity		$ 23,469	$ 36,977	$ (43)	$ 640	$ (35,143)
Balance, beginning of period at Dec. 31, 2019		23,469	36,977	$ (43)	640	(35,143)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		64
Compensation amortization under share-based plans and other changes		113
Net income	$ 1,387		1,387
Dividends			(646)
Other			4
Other comprehensive income (loss)	1,498				1,498
Treasury stock acquired — share repurchase authorizations						(425)
Net shares acquired related to employee share-based compensation plans						(46)
Balance, end of period at Sep. 30, 2020	27,849	23,646	37,679		2,138	(35,614)
Balance, beginning of year (in shares) at Dec. 31, 2019							255.5
Common shares outstanding
Treasury stock acquired - share repurchase authorizations (in shares)							(3.5)
Net shares issued under employee share-based compensation plans (in shares)							1.3
Balance, end of period (in shares) at Sep. 30, 2020							253.3
Shareholders' Equity [Roll Forward]
Shareholders' equity		23,606	37,069		1,882	(35,614)
Balance, beginning of period at Jun. 30, 2020		23,606	37,069		1,882	(35,614)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		8
Compensation amortization under share-based plans and other changes		32
Net income	827		827
Dividends			(218)
Other			1
Other comprehensive income (loss)	256				256
Treasury stock acquired — share repurchase authorizations						0
Net shares acquired related to employee share-based compensation plans						0
Balance, end of period at Sep. 30, 2020	27,849	23,646	37,679		2,138	(35,614)
Balance, beginning of year (in shares) at Jun. 30, 2020							253.2
Common shares outstanding
Treasury stock acquired - share repurchase authorizations (in shares)							0.0
Net shares issued under employee share-based compensation plans (in shares)							0.1
Balance, end of period (in shares) at Sep. 30, 2020							253.3
Shareholders' Equity [Roll Forward]
Shareholders' equity	27,849	23,646	37,679		2,138	(35,614)
Shareholders' equity	29,201	23,743	38,771		2,502	(35,815)
Balance, beginning of period at Dec. 31, 2020	29,201	23,743	38,771		2,502	(35,815)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		214
Compensation amortization under share-based plans and other changes		127
Net income	2,329		2,329
Dividends			(660)
Other			(2)
Other comprehensive income (loss)	(1,336)				(1,336)
Treasury stock acquired — share repurchase authorizations	(1,360)					(1,356)
Net shares acquired related to employee share-based compensation plans	(43)					(43)
Balance, end of period at Sep. 30, 2021	$ 28,474	24,084	40,438		1,166	(37,214)
Balance, beginning of year (in shares) at Dec. 31, 2020	252.4						252.4
Common shares outstanding
Treasury stock acquired - share repurchase authorizations (in shares)	(8.8)						(8.8)
Net shares issued under employee share-based compensation plans (in shares)							2.4
Balance, end of period (in shares) at Sep. 30, 2021	246.0						246.0
Shareholders' Equity [Roll Forward]
Shareholders' equity		24,002	39,998		1,769	(36,613)
Balance, beginning of period at Jun. 30, 2021		24,002	39,998		1,769	(36,613)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		45
Compensation amortization under share-based plans and other changes		37
Net income	$ 662		662
Dividends			(220)
Other			(2)
Other comprehensive income (loss)	(603)				(603)
Treasury stock acquired — share repurchase authorizations	(600)					(600)
Net shares acquired related to employee share-based compensation plans	(1)					(1)
Balance, end of period at Sep. 30, 2021	$ 28,474	24,084	40,438		1,166	(37,214)
Balance, beginning of year (in shares) at Jun. 30, 2021							249.5
Common shares outstanding
Treasury stock acquired - share repurchase authorizations (in shares)	(3.8)						(3.8)
Net shares issued under employee share-based compensation plans (in shares)							0.3
Balance, end of period (in shares) at Sep. 30, 2021	246.0						246.0
Shareholders' Equity [Roll Forward]
Shareholders' equity	$ 28,474	$ 24,084	$ 40,438		$ 1,166	$ (37,214)