Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 1,198	$ 1,235	$ 743
Net unrealized holding gains (losses) arising during the period	257	(69)	(81)
Less reclassification adjustment for net securities losses included in net income	(8)	(20)	0
Less net losses realized as a yield adjustment in interest on investment securities	0	0	(3)
Change in net unrealized gains (losses) before income taxes	265	(49)	(78)
Change in net cash flow hedge gains before income taxes	44	0	0
Actuarial gain (loss) arising during the period	163	(191)	72
Amortization of actuarial net loss	(42)	(61)	(51)
Amortization of prior service credit	(27)	(27)	(27)
Change in defined benefit pension and other postretirement plans adjustment before income taxes	178	(157)	96
Total other comprehensive income (loss) before income taxes	487	(206)	18
Provision (benefit) for income taxes	113	(47)	(1)
Total other comprehensive income (loss), net of tax	374	(159)	19
Comprehensive Income	$ 1,572	$ 1,076	$ 762