Loans, Leases, and Allowance for Credit Losses (Summary of Changes in the Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Allowance for loan losses
Balance at beginning of period	$ 535	$ 860	$ 777	$ 497
Provision for loan losses	(45)	45	(281)	446
Gross loan and lease charge-offs	8	58	37	107
Recoveries	9	6	32	17
Net loan and lease charge-offs (recoveries)	(1)	52	5	90
Balance at end of period	491	853	491	853
Reserve for unfunded lending commitments
Balance at beginning of period	39	54	58	29
Provision for unfunded lending commitments	(1)	10	(20)	35
Balance at end of period	38	64	38	64
Total allowance for credit losses	529	917	529	917
Commercial
Allowance for loan losses
Balance at beginning of period	321	571	464	282
Provision for loan losses	(25)	41	(162)	364
Gross loan and lease charge-offs	4	54	27	95
Recoveries	7	4	24	11
Net loan and lease charge-offs (recoveries)	(3)	50	3	84
Balance at end of period	299	562	299	562
Reserve for unfunded lending commitments
Balance at beginning of period	21	27	30	11
Provision for unfunded lending commitments	(2)	14	(11)	30
Balance at end of period	19	41	19	41
Total allowance for credit losses	318	603	318	603
Commercial real estate
Allowance for loan losses
Balance at beginning of period	111	144	171	69
Provision for loan losses	(10)	6	(70)	81
Gross loan and lease charge-offs	0	1	0	1
Recoveries	0	0	0	0
Net loan and lease charge-offs (recoveries)	0	1	0	1
Balance at end of period	101	149	101	149
Reserve for unfunded lending commitments
Balance at beginning of period	10	20	20	12
Provision for unfunded lending commitments	0	(4)	(10)	4
Balance at end of period	10	16	10	16
Total allowance for credit losses	111	165	111	165
Consumer
Allowance for loan losses
Balance at beginning of period	103	145	142	146
Provision for loan losses	(10)	(2)	(49)	1
Gross loan and lease charge-offs	4	3	10	11
Recoveries	2	2	8	6
Net loan and lease charge-offs (recoveries)	2	1	2	5
Balance at end of period	91	142	91	142
Reserve for unfunded lending commitments
Balance at beginning of period	8	7	8	6
Provision for unfunded lending commitments	1	0	1	1
Balance at end of period	9	7	9	7
Total allowance for credit losses	$ 100	$ 149	$ 100	$ 149