Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 2,697	$ 2,622	$ 2,523
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income	2,331	2,994	(1,489)
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income	(9)	(4)	(27)
Net changes in benefit plan assets and obligations	18	33	(56)
Net changes in unrealized foreign currency translation	12	117	(247)
Other comprehensive income (loss) before income taxes	2,352	3,140	(1,819)
Income tax expense (benefit)	490	641	(349)
Other comprehensive income (loss), net of taxes	1,862	2,499	(1,470)
Comprehensive income	$ 4,559	$ 5,121	$ 1,053