Consolidated Statement of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 669	$ 617
Other comprehensive income (loss):
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	(1,203)	144
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	(2)
Net changes in benefit plan assets and obligations	22	17
Net changes in unrealized foreign currency translation	6	41
Other comprehensive income (loss) before income taxes	(1,177)	202
Income tax expense (benefit)	(244)	62
Other comprehensive income (loss), net of taxes	(933)	140
Comprehensive income (loss)	$ (264)	$ 757