Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 873	$ 396	$ 557	$ 796	$ 621	$ 709	$ 524	$ 669	$ 2,622	$ 2,523	$ 2,056
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income									2,994	(1,489)	294
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income									(4)	(27)	8
Net changes in benefit plan assets and obligations									33	(56)	29
Net changes in unrealized foreign currency translation									117	(247)	191
Other comprehensive income (loss) before income taxes									3,140	(1,819)	522
Income tax expense (benefit)									641	(349)	110
Other comprehensive income (loss), net of taxes									2,499	(1,470)	412
Comprehensive income									$ 5,121	$ 1,053	$ 2,468