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 (loss), net of tax [Member]	Treasury stock, at cost [Member]	Common shares outstanding [Member]
Shareholders' Equity [Roll Forward]
Shareholders' equity		$ 23,144	$ 35,204		$ (1,859)	$ (33,595)
Balance, beginning of year at Dec. 31, 2018		23,144	35,204		(1,859)	(33,595)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		54
Compensation amortization under share-based plans and other changes		45
Shareholders' equity	$ 24,340	23,243	35,795		(682)	(34,016)
Net income	796		796
Dividends			(204)
Other			(1)
Other comprehensive income (loss)	1,177				1,177
Treasury stock acquired — share repurchase authorization						(375)
Net shares acquired related to employee share-based compensation plans						(46)
Balance, end of period at Mar. 31, 2019	24,340	23,243	35,795		(682)	(34,016)
Balance, beginning of year (in shares) at Dec. 31, 2018							263.6
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)							(2.9)
Net shares issued under employee share-based compensation plans (in shares)							1.2
Balance, end of period (in shares) at Mar. 31, 2019							261.9
Shareholders' Equity [Roll Forward]
Shareholders' equity	24,340	23,243	35,795		(682)	(34,016)
Shareholders' equity	25,943	23,469	36,977		640	(35,143)
Shareholders' equity | Accounting Standards Update 2016-13 [Member]				$ (43)
Balance, beginning of year at Dec. 31, 2019	25,943	23,469	36,977		640	(35,143)
Balance, beginning of year (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019				(43)
Shareholders' Equity [Roll Forward]
Employee share-based compensation		27
Compensation amortization under share-based plans and other changes		46
Shareholders' equity	25,943	23,542	37,325		(49)	(35,614)
Shareholders' equity | Accounting Standards Update 2016-13 [Member]				$ (43)
Net income	600		600
Dividends			(210)
Other			1
Other comprehensive income (loss)	(689)				(689)
Treasury stock acquired — share repurchase authorization	(425)					(425)
Net shares acquired related to employee share-based compensation plans	(46)					(46)
Balance, end of period at Mar. 31, 2020	$ 25,204	23,542	37,325		(49)	(35,614)
Balance, beginning of year (in shares) at Dec. 31, 2019	255.5						255.5
Common shares outstanding
Treasury stock acquired - share repurchase authorization (in shares)	(3.5)						(3.5)
Net shares issued under employee share-based compensation plans (in shares)							0.8
Balance, end of period (in shares) at Mar. 31, 2020	252.8						252.8
Shareholders' Equity [Roll Forward]
Shareholders' equity	$ 25,204	$ 23,542	$ 37,325		$ (49)	$ (35,614)