Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 791	$ 426
OCI, net of tax:
Change in unrecognized net pension and postretirement costs	14	9
Change in unrealized net gains (losses) on cash flow hedges	78	(2)
Change in unrealized net gains (losses) on AFS securities	(268)	(2)
Other, net	(2)	2
Total OCI	(178)	7
Total comprehensive income	613	433
Income Tax Effect of Items Included in OCI:
Change in unrecognized net pension and postretirement costs	4	7
Change in unrealized net gains (losses) on cash flow hedges	26	(1)
Change in unrealized net gains (losses) on AFS securities	(84)	(1)
Other, net	$ 1	$ 0