Asset Quality - Changes in Allowance for Loan and Lease Losses by Loan Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 1,708	$ 890	$ 900	$ 883
Provision	150	199	934	335
Charge-offs	(151)	(213)	(362)	(384)
Recoveries	23	17	54	59
Ending balance	1,730	893	1,730	893
Total ALLL, including discontinued operations	1,772	904	1,772	904	$ 1,751	$ 910	$ 902	$ 897
Total provision, including discontinued operations	149	198	936	338
Total charge-offs, including discontinued operations	(151)	(214)	(366)	(393)
Total recoveries, including discontinued operations	23	18	57	62
Provision for losses on lending-related commitments	10	1	67	1
Amount realized from fraud incident		123
Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,113	747	751	743
Provision	181	169	797	252
Charge-offs	(124)	(177)	(266)	(277)
Recoveries	11	7	23	28
Ending balance	1,181	746	1,181	746
Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	595	143	149	140
Provision	(31)	30	137	83
Charge-offs	(27)	(36)	(96)	(107)
Recoveries	12	10	31	31
Ending balance	549	147	549	147
Commercial and industrial | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	725	549	551	532
Provision	177	175	613	242
Charge-offs	(101)	(176)	(232)	(242)
Recoveries	9	6	19	22
Ending balance	810	554	810	554
Commercial mortgage | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	292	139	143	142
Provision	(2)	(5)	135	(4)
Charge-offs	(13)	0	(18)	(6)
Recoveries	2	0	3	2
Ending balance	279	134	279	134
Real estate — construction | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	41	24	22	33
Provision	(7)	(1)	19	(6)
Charge-offs	0	0	0	(4)
Recoveries	0	0	0	0
Ending balance	34	23	34	23
Commercial real estate loans | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	333	163	165	175
Provision	(9)	(6)	154	(10)
Charge-offs	(13)	0	(18)	(10)
Recoveries	2	0	3	2
Ending balance	313	157	313	157
Commercial lease financing | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	55	35	35	36
Provision	13	0	30	20
Charge-offs	(10)	(1)	(16)	(25)
Recoveries	0	1	1	4
Ending balance	58	35	58	35
Real estate — residential mortgage | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	101	7	7	7
Provision	2	1	21	2
Charge-offs	0	(1)	(2)	(3)
Recoveries	1	0	1	1
Ending balance	104	7	104	7
Home equity loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	197	36	31	35
Provision	(13)	1	9	8
Charge-offs	(4)	(6)	(10)	(16)
Recoveries	3	2	6	6
Ending balance	183	33	183	33
Consumer direct loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	130	32	34	30
Provision	1	10	52	29
Charge-offs	(8)	(10)	(30)	(30)
Recoveries	2	2	6	5
Ending balance	125	34	125	34
Credit cards | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	107	44	47	48
Provision	(5)	11	39	26
Charge-offs	(9)	(11)	(32)	(34)
Recoveries	2	2	6	6
Ending balance	95	46	95	46
Consumer indirect loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	60	24	30	20
Provision	(16)	7	16	18
Charge-offs	(6)	(8)	(22)	(24)
Recoveries	4	4	12	13
Ending balance	42	27	42	27
Discontinued operations
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	43	12	10	14
Provision	(1)	(1)	2	3
Charge-offs	0	(1)	(4)	(9)
Recoveries	0	1	3	3
Ending balance	$ 42	$ 11	42	$ 11
Impact of ASC 326 Adoption
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			204
Total ALLL, including discontinued operations						235
Impact of ASC 326 Adoption | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			(124)
Impact of ASC 326 Adoption | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			328
Impact of ASC 326 Adoption | Commercial and industrial | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			(141)
Impact of ASC 326 Adoption | Commercial mortgage | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			16
Impact of ASC 326 Adoption | Real estate — construction | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			(7)
Impact of ASC 326 Adoption | Commercial real estate loans | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			9
Impact of ASC 326 Adoption | Commercial lease financing | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			8
Impact of ASC 326 Adoption | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			77
Impact of ASC 326 Adoption | Home equity loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			147
Impact of ASC 326 Adoption | Consumer direct loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			63
Impact of ASC 326 Adoption | Credit cards | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			35
Impact of ASC 326 Adoption | Consumer indirect loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			6
Impact of ASC 326 Adoption | Discontinued operations
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			31
As Reported Under ASC 326
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			1,104
Total ALLL, including discontinued operations						$ 1,145
As Reported Under ASC 326 | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			627
As Reported Under ASC 326 | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			477
As Reported Under ASC 326 | Commercial and industrial | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			410
As Reported Under ASC 326 | Commercial mortgage | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			159
As Reported Under ASC 326 | Real estate — construction | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			15
As Reported Under ASC 326 | Commercial real estate loans | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			174
As Reported Under ASC 326 | Commercial lease financing | Commercial Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			43
As Reported Under ASC 326 | Real estate — residential mortgage | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			84
As Reported Under ASC 326 | Home equity loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			178
As Reported Under ASC 326 | Consumer direct loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			97
As Reported Under ASC 326 | Credit cards | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			82
As Reported Under ASC 326 | Consumer indirect loans | Consumer Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			36
As Reported Under ASC 326 | Discontinued operations
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance			$ 41