Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Investment securities, Balance at beginning of period, net of tax	$ (138)		$ (101)	$ (33)
Cumulative effect of change in accounting principle	0		1	0
Net unrealized holding gains (losses) arising during the period	257		(69)	(81)
Investment securities, Less: Benefit for income taxes	60		(16)	(27)
Investment securities, Net unrealized holding losses arising during period, net of tax	197		(53)	(54)
Investment securities, Net realized (losses) gains included in net securities (losses) gains	(8)		(20)	0
Investment securities, Less: Benefit for income taxes	(2)		(5)	0
Investment securities, Reclassification adjustment for net securities (losses) gains included in net income, net of tax	(6)		(15)	0
Investment securities, Net losses realized as a yield adjustment in interest on investment securities	0		0	(3)
Investment securities, Less: Benefit for income taxes	0		0	(1)
Investment securities, Reclassification adjustment for net losses realized as a yield adjustment included in net income, net of tax	0		0	(2)
Investment securities, Change in net unrealized losses on investment securities, net of tax	203		(38)	(52)
Investment securities, Reclassification of certain deferred tax effects	0		0	(16)	[1]
Investment securities, Balance at end of period, net of tax	65		(138)	(101)
Cash Flow Hedges, Balance at beginning of period, net of tax	0		0	0
Cash flow hedges, Net gain arising during the period	44		0	0
Cash flow hedges, Less: Provision for income tax	10		0	0
Change in net cash flow hedges gains, net of tax	34		0	0
Cash Flow Hedges, Balance at end of period, net of tax	34	[2]	0	0
Benefit plans, Balance at beginning of period, net of tax	(471)		(350)	(350)
Benefit plans, Actuarial loss arising during the period	163		(191)	72
Benefit plans, Less: Provision (benefit) for income taxes	38		(44)	17
Benefit plans, Net defined benefit pension and other postretirement adjustment arising during the period, net of tax	125		(147)	55
Benefit plans, Amortization of actuarial net loss	42		61	51
Benefit plans, Amortization of prior service (credit) cost	(27)		(27)	(27)
Benefit plans, Total amounts recognized in employee benefits expense	15		34	24
Benefit plans, Less: Provision for income taxes	3		8	8
Benefit plans, Adjustment for amounts recognized as components of net periodic benefit cost during the period, net of tax	12		26	16
Benefit plans, Change in defined benefit pension and other postretirement plans adjustment, net of tax	137		(121)	71
Benefit plans, Reclassification of certain deferred tax effects	0		0	(71)	[1]
Benefit plans, Balance at end of period, net of tax	(334)		(471)	(350)
Total accumulated other comprehensive loss at end of period, net of tax	$ (235)		$ (609)	$ (451)

[1] Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. For further information, refer to Note 1.

[2] Return on average assets is calculated based on the greater of average assets or average liabilities and attributed equity.