Loans, Leases, and Allowance for Credit Losses (Summary of Selected Information on TDRs) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	$ 352	$ 311
Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	37	18
Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	34	4
Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	11	12
Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	52	39
Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	68	116
Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	150	122
Accruing
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	231	198
Accruing | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	13	10
Accruing | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	32	3
Accruing | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	9	10
Accruing | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	35	20
Accruing | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	57	103
Accruing | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	85	52
Accruing | Commercial
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	95	29
Accruing | Commercial | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	7	5
Accruing | Commercial | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	4	1
Accruing | Commercial | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	8	4
Accruing | Commercial | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	15	7
Accruing | Commercial | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	61	12
Accruing | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	17	7
Accruing | Commercial | Commercial and industrial | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	0
Accruing | Commercial | Commercial and industrial | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial | Commercial and industrial | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial | Commercial and industrial | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial | Commercial and industrial | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	3
Accruing | Commercial | Commercial and industrial | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	15	4
Accruing | Commercial | Owner-occupied
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	78	22
Accruing | Commercial | Owner-occupied | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	5
Accruing | Commercial | Owner-occupied | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	4	1
Accruing | Commercial | Owner-occupied | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial | Owner-occupied | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	8	4
Accruing | Commercial | Owner-occupied | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	15	4
Accruing | Commercial | Owner-occupied | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	46	8
Accruing | Commercial real estate
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	103	134
Accruing | Commercial real estate | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Accruing | Commercial real estate | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	26	0
Accruing | Commercial real estate | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial real estate | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	27	16
Accruing | Commercial real estate | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	41	94
Accruing | Commercial real estate | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	8	23
Accruing | Commercial real estate | Construction and land development
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Construction and land development | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0
Accruing | Commercial real estate | Term
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	103	134
Accruing | Commercial real estate | Term | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Accruing | Commercial real estate | Term | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	26	0
Accruing | Commercial real estate | Term | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Commercial real estate | Term | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	27	16
Accruing | Commercial real estate | Term | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	41	94
Accruing | Commercial real estate | Term | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	8	23
Accruing | Consumer
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	33	35
Accruing | Consumer | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	4
Accruing | Consumer | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Accruing | Consumer | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	9	10
Accruing | Consumer | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Consumer | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	2
Accruing | Consumer | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	16	17
Accruing | Consumer | Home equity credit line
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	9	10
Accruing | Consumer | Home equity credit line | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Consumer | Home equity credit line | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Accruing | Consumer | Home equity credit line | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	6	7
Accruing | Consumer | Home equity credit line | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Consumer | Home equity credit line | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Consumer | Home equity credit line | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Accruing | Consumer | 1-4 family residential
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	24	25
Accruing | Consumer | 1-4 family residential | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	4
Accruing | Consumer | 1-4 family residential | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Accruing | Consumer | 1-4 family residential | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	3	3
Accruing | Consumer | 1-4 family residential | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Accruing | Consumer | 1-4 family residential | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	2
Accruing | Consumer | 1-4 family residential | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	14	15
Nonaccruing
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	121	113
Nonaccruing | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	24	8
Nonaccruing | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	1
Nonaccruing | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Nonaccruing | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	17	19
Nonaccruing | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	11	13
Nonaccruing | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	65	70
Nonaccruing | Commercial
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	94	83
Nonaccruing | Commercial | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	22	5
Nonaccruing | Commercial | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	0
Nonaccruing | Commercial | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	6
Nonaccruing | Commercial | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	7	10
Nonaccruing | Commercial | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	59	62
Nonaccruing | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	69	65
Nonaccruing | Commercial | Commercial and industrial | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	17	0
Nonaccruing | Commercial | Commercial and industrial | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	0
Nonaccruing | Commercial | Commercial and industrial | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial | Commercial and industrial | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	3
Nonaccruing | Commercial | Commercial and industrial | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	7	10
Nonaccruing | Commercial | Commercial and industrial | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	42	52
Nonaccruing | Commercial | Owner-occupied
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	25	18
Nonaccruing | Commercial | Owner-occupied | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	5
Nonaccruing | Commercial | Owner-occupied | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial | Owner-occupied | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial | Owner-occupied | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	3	3
Nonaccruing | Commercial | Owner-occupied | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial | Owner-occupied | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	17	10
Nonaccruing | Commercial real estate
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	21	20
Nonaccruing | Commercial real estate | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Nonaccruing | Commercial real estate | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial real estate | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial real estate | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	12	13
Nonaccruing | Commercial real estate | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	4	3
Nonaccruing | Commercial real estate | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	3	2
Nonaccruing | Commercial real estate | Term
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	21	20
Nonaccruing | Commercial real estate | Term | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Nonaccruing | Commercial real estate | Term | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial real estate | Term | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Commercial real estate | Term | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	12	13
Nonaccruing | Commercial real estate | Term | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	4	3
Nonaccruing | Commercial real estate | Term | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	3	2
Nonaccruing | Consumer
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	6	10
Nonaccruing | Consumer | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	1
Nonaccruing | Consumer | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Nonaccruing | Consumer | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	2	2
Nonaccruing | Consumer | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	3	6
Nonaccruing | Consumer | Home equity credit line
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	2
Nonaccruing | Consumer | Home equity credit line | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Home equity credit line | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Home equity credit line | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	2
Nonaccruing | Consumer | Home equity credit line | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Home equity credit line | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | Home equity credit line | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | 1-4 family residential
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	5	8
Nonaccruing | Consumer | 1-4 family residential | Interest rate below market
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	1
Nonaccruing | Consumer | 1-4 family residential | Maturity or term extension
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	1
Nonaccruing | Consumer | 1-4 family residential | Principal forgiveness
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	1	0
Nonaccruing | Consumer | 1-4 family residential | Payment deferral
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | 1-4 family residential | Other
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	0	0
Nonaccruing | Consumer | 1-4 family residential | Multiple modification types
Financing Receivable, Modifications [Line Items]
Amortized cost resulting from the following modification types	$ 3	$ 6