Consolidated Statement of Changes in Shareholders' Equity - 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 (loss), net of tax [Member]	Accumulated other comprehensive income (loss), net of tax [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Treasury stock, at cost [Member]	Common shares outstanding [Member]
Shareholders' Equity [Roll Forward]
Shareholders' equity		$ 22,886	$ 33,462	$ 22	$ (343)	$ (22)	$ (32,274)
Balance, beginning of year at Dec. 31, 2017		22,886	33,462	22	(343)	(22)	(32,274)
Shareholders' Equity [Roll Forward]
Shareholders' equity		22,886	33,462	22	(343)	(22)	(32,274)
Reclassification of certain tax effects from adoption of updated accounting guidance			24		(24)
Balance, end of year at Jan. 01, 2018				22		(22)
Balance, beginning of year (in shares) at Dec. 31, 2017								271.4
Balance, beginning of year at Dec. 31, 2017		22,886	33,462	22	(343)	(22)	(32,274)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		108
Compensation amortization under share-based plans and other changes		150
Shareholders' equity	$ 22,894	22,886	33,462	22	(343)	(22)	(32,274)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201601Member
Net income	$ 2,523		2,523
Dividends			(818)
Other			(9)
Other comprehensive income (loss)	(1,470)				(1,470)
Treasury stock acquired — share repurchase authorization							(1,270)
Net shares acquired related to employee share-based compensation plans							(51)
Balance, end of year at Dec. 31, 2018	22,894	23,144	35,204		(1,859)		(33,595)
Balance, beginning of year (in shares) at Dec. 31, 2017								271.4
Common shares outstanding
Treasury stock acquired — share repurchase authorization (in shares)								(9.6)
Net shares issued under employee share-based compensation plans (in shares)								1.8
Balance, end of year (in shares) at Dec. 31, 2018								263.6
Shareholders' Equity [Roll Forward]
Shareholders' equity				22		$ (22)
Shareholders' equity	22,894	23,144	35,204		(1,859)		(33,595)
Employee share-based compensation		180
Compensation amortization under share-based plans and other changes		145
Shareholders' equity	22,894	23,144	35,204	(43)	640		(33,595)
Net income	2,622		2,622
Dividends			(848)
Other			(1)
Other comprehensive income (loss)	2,499				2,499
Treasury stock acquired — share repurchase authorization							(1,500)
Net shares acquired related to employee share-based compensation plans	(48)						(48)
Balance, end of year at Dec. 31, 2019	$ 25,943	23,469	36,977	(43)	640		(35,143)
Common shares outstanding
Treasury stock acquired — share repurchase authorization (in shares)								(10.8)
Net shares issued under employee share-based compensation plans (in shares)								2.7
Balance, end of year (in shares) at Dec. 31, 2019	255.5							255.5
Shareholders' Equity [Roll Forward]
Shareholders' equity	$ 25,943	23,469	36,977	(43)	640		(35,143)
Employee share-based compensation		123
Compensation amortization under share-based plans and other changes		151
Shareholders' equity	$ 29,201	23,743	38,771	$ (43)	2,502		(35,815)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 2,697		2,697
Dividends			(864)
Other			4
Other comprehensive income (loss)	1,862				1,862
Treasury stock acquired — share repurchase authorization	(625)						(625)
Net shares acquired related to employee share-based compensation plans	(47)						(47)
Balance, end of year at Dec. 31, 2020	$ 29,201	23,743	38,771		2,502		(35,815)
Common shares outstanding
Treasury stock acquired — share repurchase authorization (in shares)	(4.9)							(4.9)
Net shares issued under employee share-based compensation plans (in shares)								1.8
Balance, end of year (in shares) at Dec. 31, 2020	252.4							252.4
Shareholders' Equity [Roll Forward]
Shareholders' equity	$ 29,201	$ 23,743	$ 38,771		$ 2,502		$ (35,815)