Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Current	$ 104,893	$ 93,197
Days Past Due	1,266	1,003
Purchased Credit Impaired		446
Total	106,159	94,646
Accrued interest	225	244
Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	77,316	67,224
Days Past Due	889	635
Purchased Credit Impaired		173
Total	78,205	68,032
Accrued interest	121
Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	27,577	25,973
Days Past Due	377	368
Purchased Credit Impaired		273
Total	27,954	26,614
Accrued interest	104
Commercial and industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	57,659	47,768
Days Past Due	638	479
Purchased Credit Impaired		48
Total	58,297	48,295
Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	13,269	13,258
Days Past Due	196	109
Purchased Credit Impaired		124
Total	13,465	13,491
Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	1,916	1,551
Days Past Due	3	6
Purchased Credit Impaired		1
Total	1,919	1,558
Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	15,185	14,809
Days Past Due	199	115
Purchased Credit Impaired		125
Total	15,384	15,049
Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Current	4,472	4,647
Days Past Due	52	41
Purchased Credit Impaired		0
Total	4,524	4,688
Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	8,039	6,705
Days Past Due	110	61
Purchased Credit Impaired		257
Total	8,149	7,023
Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	9,592	10,071
Days Past Due	190	190
Purchased Credit Impaired		13
Total	9,782	10,274
Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	4,306	3,484
Days Past Due	21	26
Purchased Credit Impaired		3
Total	4,327	3,513
Credit cards | Commercial Loans
Financing Receivable, Past Due [Line Items]
Total	132	144
Credit cards | Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	957	1,104
Days Past Due	17	26
Purchased Credit Impaired		0
Total	974	1,130
Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Current	4,683	4,609
Days Past Due	39	65
Purchased Credit Impaired		0
Total	4,722	4,674
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Days Past Due	280	228
30-59 Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	208	143
30-59 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	72	85
30-59 Days Past Due | Commercial and industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	116	110
30-59 Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	52	8
30-59 Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	0	3
30-59 Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	52	11
30-59 Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	40	22
30-59 Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	16	7
30-59 Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	31	30
30-59 Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	9	10
30-59 Days Past Due | Credit cards | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	6
30-59 Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	13	32
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Days Past Due	139	101
60-89 Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	112	68
60-89 Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	27	33
60-89 Days Past Due | Commercial and industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	71	52
60-89 Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	41	5
60-89 Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	0	0
60-89 Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	41	5
60-89 Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	0	11
60-89 Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	5	5
60-89 Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	12	10
60-89 Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	4	5
60-89 Days Past Due | Credit cards | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	5
60-89 Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	8
90 and Greater Days Past Due
Financing Receivable, Past Due [Line Items]
Days Past Due	87	97
90 and Greater Days Past Due | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	64	69
90 and Greater Days Past Due | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	23	28
90 and Greater Days Past Due | Commercial and industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	47	53
90 and Greater Days Past Due | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	12	13
90 and Greater Days Past Due | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	2	1
90 and Greater Days Past Due | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	14	14
90 and Greater Days Past Due | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	2
90 and Greater Days Past Due | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	0	1
90 and Greater Days Past Due | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	6	5
90 and Greater Days Past Due | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	5	7
90 and Greater Days Past Due | Credit cards | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	9	12
90 and Greater Days Past Due | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	3
Nonperforming financial instruments
Financing Receivable, Past Due [Line Items]
Days Past Due	760	577
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	505	355
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	255	222
Nonperforming financial instruments | Commercial and industrial | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	404	264
Nonperforming financial instruments | Commercial mortgage | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	91	83
Nonperforming financial instruments | Commercial real estate: Construction | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	1	2
Nonperforming financial instruments | Commercial real estate loans | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	92	85
Nonperforming financial instruments | Commercial lease financing | Commercial Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	9	6
Nonperforming financial instruments | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	89	48
Nonperforming financial instruments | Home equity loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	141	145
Nonperforming financial instruments | Consumer direct loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	3	4
Nonperforming financial instruments | Credit cards | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	2	3
Nonperforming financial instruments | Consumer indirect loans | Consumer Loans
Financing Receivable, Past Due [Line Items]
Days Past Due	$ 20	$ 22