Consolidated Statement of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 557	$ 524	$ 1,353	$ 1,193
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income	1,108	(298)	2,524	(1,501)
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income	(4)	(12)	1	(14)
Net changes in benefit plan assets and obligations	14	21	26	43
Net changes in unrealized foreign currency translation	5	(158)	55	(152)
Other comprehensive income (loss) before income taxes	1,123	(447)	2,606	(1,624)
Income tax expense (benefit)	235	(81)	541	(325)
Other comprehensive income (loss), net of taxes	888	(366)	2,065	(1,299)
Comprehensive income (loss)	$ 1,445	$ 158	$ 3,418	$ (106)