Consolidated Statements Of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 884	$ 592	$ 469
Other comprehensive income (loss), net of tax:
Net unrealized holding gains (losses) on investment securities	(113)	(2)	(74)
Net unrealized gains on other noninterest-bearing investments	2	3	2
Net unrealized holding gains (losses) on derivative instruments	(4)	(3)	5
Reclassification adjustment for increase in interest income recognized in earnings on derivative instruments	3	(2)	(7)
Pension and postretirement	(1)	(12)	(7)
Effect of new tax rates from Tax Cuts and Jobs Act of 2017	0	25	0
Other Comprehensive Income (Loss), Net of Tax	(111)	(17)	(67)
Comprehensive income	$ 773	$ 575	$ 402