Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 662	$ 827	$ 2,329	$ 1,387
Other comprehensive income (loss)
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	(686)	217	(1,749)	2,001
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	0	(7)	0	(10)
Net changes in benefit plan assets and obligations	26	20	77	64
Net changes in unrealized foreign currency translation	(91)	79	(25)	(137)
Other comprehensive income (loss) before income taxes	(751)	309	(1,697)	1,918
Income tax expense (benefit)	(148)	53	(361)	420
Other comprehensive income (loss), net of taxes	(603)	256	(1,336)	1,498
Comprehensive income	$ 59	$ 1,083	$ 993	$ 2,885