Loans, Leases, and Allowance for Credit Losses (Summary of Changes in the Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Allowance for loan losses
Balance at beginning of period	$ 646	$ 730	$ 777	$ 497
Provision for loan losses	(113)	161	(236)	401
Gross loan and lease charge-offs	8	36	29	49
Recoveries	10	5	23	11
Net loan and lease charge-offs (recoveries)	(2)	31	6	38
Balance at end of period	535	860	535	860
Reserve for unfunded lending commitments
Balance at beginning of period	49	47	58	29
Provision for unfunded lending commitments	(10)	7	(19)	25
Balance at end of period	39	54	39	54
Total allowance for credit losses	574	914	574	914
Commercial
Allowance for loan losses
Balance at beginning of period	362	413	464	282
Provision for loan losses	(43)	186	(137)	323
Gross loan and lease charge-offs	5	31	23	41
Recoveries	7	3	17	7
Net loan and lease charge-offs (recoveries)	(2)	28	6	34
Balance at end of period	321	571	321	571
Reserve for unfunded lending commitments
Balance at beginning of period	24	16	30	11
Provision for unfunded lending commitments	(3)	11	(9)	16
Balance at end of period	21	27	21	27
Total allowance for credit losses	342	598	342	598
Commercial real estate
Allowance for loan losses
Balance at beginning of period	152	128	171	69
Provision for loan losses	(41)	16	(60)	75
Gross loan and lease charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net loan and lease charge-offs (recoveries)	0	0	0	0
Balance at end of period	111	144	111	144
Reserve for unfunded lending commitments
Balance at beginning of period	17	23	20	12
Provision for unfunded lending commitments	(7)	(3)	(10)	8
Balance at end of period	10	20	10	20
Total allowance for credit losses	121	164	121	164
Consumer
Allowance for loan losses
Balance at beginning of period	132	189	142	146
Provision for loan losses	(29)	(41)	(39)	3
Gross loan and lease charge-offs	3	5	6	8
Recoveries	3	2	6	4
Net loan and lease charge-offs (recoveries)	0	3	0	4
Balance at end of period	103	145	103	145
Reserve for unfunded lending commitments
Balance at beginning of period	8	8	8	6
Provision for unfunded lending commitments	0	(1)	0	1
Balance at end of period	8	7	8	7
Total allowance for credit losses	$ 111	$ 152	$ 111	$ 152