Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 621	$ 709	$ 524	$ 669	$ 551	$ 293	$ 595	$ 617	$ 2,523	$ 2,056	$ 3,014
Other comprehensive income (loss):
Changes in net unrealized gains (losses) on investment securities having no credit losses recognized in the consolidated statement of income									(1,489)	294	(883)
Changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income									(27)	8	21
Net changes in benefit plan assets and obligations									(56)	29	16
Net changes in unrealized foreign currency translation									(247)	191	(41)
Other comprehensive income (loss) before income taxes									(1,819)	522	(887)
Income tax expense (benefit)									(349)	110	(289)
Other comprehensive income (loss), net of taxes									(1,470)	412	(598)
Comprehensive income									$ 1,053	$ 2,468	$ 2,416