Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 1,063	$ 798
OCI, net of tax:
Change in unrecognized net pension and postretirement costs	15	17
Change in unrealized net gains (losses) on cash flow hedges	11	(34)
Change in unrealized net gains (losses) on AFS securities	1,721	309
Other, net	(5)	2
Total OCI, net of tax	1,742	294
Total comprehensive income	2,805	1,092
Income Tax Effect of Items Included in OCI:
Change in unrecognized net pension and postretirement costs	5	6
Change in unrealized net gains (losses) on cash flow hedges	3	(11)
Change in unrealized net gains (losses) on AFS securities	527	95
Other, net	$ 0	$ 0