Consolidated Statement of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 524	$ 595	$ 1,193	$ 1,212
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income	(298)	327	(1,501)	471
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income	(12)	2	(14)	2
Net changes in benefit plan assets and obligations	21	17	43	34
Net changes in unrealized foreign currency translation	(158)	48	(152)	89
Other comprehensive income (loss) before income taxes	(447)	394	(1,624)	596
Income tax expense (benefit)	(81)	123	(325)	185
Other comprehensive income (loss), net of taxes	(366)	271	(1,299)	411
Comprehensive income (loss)	$ 158	$ 866	$ (106)	$ 1,623