Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 396	$ 709	$ 1,749	$ 1,902
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income	605	(414)	3,129	(1,915)
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income	(3)	(11)	(2)	(25)
Net changes in benefit plan assets and obligations	14	22	40	65
Net changes in unrealized foreign currency translation	(75)	0	(20)	(152)
Other comprehensive income (loss) before income taxes	541	(403)	3,147	(2,027)
Income tax expense (benefit)	122	(88)	663	(413)
Other comprehensive income (loss), net of taxes	419	(315)	2,484	(1,614)
Comprehensive income	$ 815	$ 394	$ 4,233	$ 288