LOANS - Credit Quality Indicators (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 685,292	$ 699,483
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	281,113	309,548
Consumer | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	48,167	47,008
Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	127,496	148,534
Consumer | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	8,524	9,223
Consumer | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	4,859	3,699
Consumer | Less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	51,613	50,094
Consumer | Less than or equal to 80% | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,362
2019	8,309
2018	2,080
2017	3,206
2016	6,570
Prior	18,621
Loans, net of unearned income	44,148	41,993
Consumer | Less than or equal to 80% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,061
Consumer | Less than or equal to 80% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	4,404
Consumer | Less than or equal to 80% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	7,465	8,101
Consumer | 80% but less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,087	4,142
Consumer | 80% but less than or equal to 100% | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	560
2019	599
2018	598
2017	420
2016	141
Prior	129
Loans, net of unearned income	2,447	3,313
Consumer | 80% but less than or equal to 100% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	39
Consumer | 80% but less than or equal to 100% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	601
Consumer | 80% but less than or equal to 100% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	640	829
Consumer | Greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	243	335
Consumer | Greater than 100% | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3
2018	26
2017	8
2016	3
Prior	22
Loans, net of unearned income	62	98
Consumer | Greater than 100% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	12
Consumer | Greater than 100% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	169
Consumer | Greater than 100% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	181	237
Consumer | LTV not available
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,748	1,660
Consumer | LTV not available | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,510	1,604
Consumer | LTV not available | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	238	56
Consumer | Total
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	56,691	56,231
Consumer | Less than 680
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	34,726	39,363
Consumer | Less than 680 | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	65
2019	205
2018	294
2017	344
2016	390
Prior	2,130
Loans, net of unearned income	3,428	3,608
Consumer | Less than 680 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	28,942	33,290
Consumer | Less than 680 | Credit cards | CANADA
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	536	629
Consumer | Less than 680 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	337
Consumer | Less than 680 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,435
Consumer | Less than 680 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,772	1,901
Consumer | Less than 680 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18
2019	113
2018	125
2017	43
2016	21
Prior	264
Loans, net of unearned income	584	564
Consumer | 680 to 760
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	68,484	77,237
Consumer | 680 to 760 | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,593
2019	2,384
2018	784
2017	973
2016	1,523
Prior	4,629
Loans, net of unearned income	11,886	13,264
Consumer | 680 to 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	52,825	59,536
Consumer | 680 to 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,053
Consumer | 680 to 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,937
Consumer | 680 to 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,990	3,530
Consumer | 680 to 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	42
2019	143
2018	114
2017	41
2016	18
Prior	425
Loans, net of unearned income	783	907
Consumer | Greater than 760
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	79,506	86,582
Consumer | Greater than 760 | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,261
2019	6,316
2018	1,619
2017	2,311
2016	4,791
Prior	11,968
Loans, net of unearned income	31,266	28,442
Consumer | Greater than 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	43,745	52,935
Consumer | Greater than 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,738
Consumer | Greater than 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,826
Consumer | Greater than 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,564	3,732
Consumer | Greater than 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	55
2019	164
2018	106
2017	43
2016	16
Prior	547
Loans, net of unearned income	931	1,473
Consumer | FICO not available
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	6,330	5,282
Consumer | FICO not available | Residential first mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,587	1,694
Consumer | FICO not available | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,984	2,773
Consumer | FICO not available | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	198	60
Consumer | FICO not available | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,561	755
Consumer | Total loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 189,046	$ 208,464