LOANS - Credit Quality Indicators (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Loans receivable
Loans, net of unearned income	$ 675,883	$ 699,483
Consumer
Loans receivable
Loans, net of unearned income	288,839	309,548
Consumer | Residential first mortgages
Loans receivable
Loans, net of unearned income	47,778	47,008
Consumer | Credit cards
Loans receivable
Loans, net of unearned income	129,813	148,534
Consumer | Home equity loans
Loans receivable
Loans, net of unearned income	7,128	9,223
Consumer | Personal, small business and other
Loans receivable
Loans, net of unearned income	4,509	3,699
Consumer | Less than or equal to 80%
Loans receivable
Loans, net of unearned income	49,851	50,094
Consumer | Less than or equal to 80% | Residential first mortgages
Loans receivable
2020	11,447
2019	7,029
2018	1,617
2017	2,711
2016	5,423
Prior	14,966
Loans, net of unearned income	43,193	41,993
Consumer | Less than or equal to 80% | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	2,876
Consumer | Less than or equal to 80% | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	3,782
Consumer | Less than or equal to 80% | Home equity loans
Loans receivable
Loans, net of unearned income	6,658	8,101
Consumer | 80% but less than or equal to 100%
Loans receivable
Loans, net of unearned income	3,185	4,142
Consumer | 80% but less than or equal to 100% | Residential first mortgages
Loans receivable
2020	1,543
2019	376
2018	507
2017	269
2016	84
Prior	66
Loans, net of unearned income	2,845	3,313
Consumer | 80% but less than or equal to 100% | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	50
Consumer | 80% but less than or equal to 100% | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	290
Consumer | 80% but less than or equal to 100% | Home equity loans
Loans receivable
Loans, net of unearned income	340	829
Consumer | Greater than 100%
Loans receivable
Loans, net of unearned income	109	335
Consumer | Greater than 100% | Residential first mortgages
Loans receivable
2020	0
2019	2
2018	11
2017	4
2016	2
Prior	16
Loans, net of unearned income	35	98
Consumer | Greater than 100% | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	16
Consumer | Greater than 100% | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	58
Consumer | Greater than 100% | Home equity loans
Loans receivable
Loans, net of unearned income	74	237
Consumer | LTV not available
Loans receivable
Loans, net of unearned income	1,761	1,660
Consumer | LTV not available | Residential first mortgages
Loans receivable
Loans, net of unearned income	1,705	1,604
Consumer | LTV not available | Home equity loans
Loans receivable
Loans, net of unearned income	56	56
Consumer | Total
Loans receivable
Loans, net of unearned income	54,906	56,231
Consumer | Less than 680
Loans receivable
Loans, net of unearned income	30,920	39,363
Consumer | Less than 680 | Residential first mortgages
Loans receivable
2020	187
2019	150
2018	246
2017	298
2016	323
Prior	1,708
Loans, net of unearned income	2,912	3,608
Consumer | Less than 680 | Credit cards
Loans receivable
Loans, net of unearned income	26,227	33,290
Consumer | Less than 680 | Credit cards | CANADA
Loans receivable
Loans, net of unearned income	572	629
Consumer | Less than 680 | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	292
Consumer | Less than 680 | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	1,055
Consumer | Less than 680 | Home equity loans
Loans receivable
Loans, net of unearned income	1,347	1,901
Consumer | Less than 680 | Personal, small business and other
Loans receivable
2020	23
2019	79
2018	82
2017	26
2016	10
Prior	214
Loans, net of unearned income	434	564
Consumer | 680 to 760
Loans receivable
Loans, net of unearned income	68,634	77,237
Consumer | 680 to 760 | Residential first mortgages
Loans receivable
2020	3,741
2019	1,857
2018	655
2017	846
2016	1,368
Prior	4,133
Loans, net of unearned income	12,600	13,264
Consumer | 680 to 760 | Credit cards
Loans receivable
Loans, net of unearned income	52,778	59,536
Consumer | 680 to 760 | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	1,014
Consumer | 680 to 760 | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	1,569
Consumer | 680 to 760 | Home equity loans
Loans receivable
Loans, net of unearned income	2,583	3,530
Consumer | 680 to 760 | Personal, small business and other
Loans receivable
2020	58
2019	106
2018	80
2017	27
2016	9
Prior	393
Loans, net of unearned income	673	907
Consumer | Greater than 760
Loans receivable
Loans, net of unearned income	84,224	86,582
Consumer | Greater than 760 | Residential first mortgages
Loans receivable
2020	9,052
2019	5,384
2018	1,227
2017	1,829
2016	3,799
Prior	9,105
Loans, net of unearned income	30,396	28,442
Consumer | Greater than 760 | Credit cards
Loans receivable
Loans, net of unearned income	49,767	52,935
Consumer | Greater than 760 | Home equity loans (pre-reset)
Loans receivable
Loans, net of unearned income	1,657
Consumer | Greater than 760 | Home equity loans (post-reset)
Loans receivable
Loans, net of unearned income	1,524
Consumer | Greater than 760 | Home equity loans
Loans receivable
Loans, net of unearned income	3,181	3,732
Consumer | Greater than 760 | Personal, small business and other
Loans receivable
2020	95
2019	134
2018	84
2017	30
2016	8
Prior	529
Loans, net of unearned income	880	1,473
Consumer | FICO not available
Loans receivable
Loans, net of unearned income	5,450	5,282
Consumer | FICO not available | Residential first mortgages
Loans receivable
Loans, net of unearned income	1,870	1,694
Consumer | FICO not available | Credit cards
Loans receivable
Loans, net of unearned income	1,041	2,773
Consumer | FICO not available | Home equity loans
Loans receivable
Loans, net of unearned income	17	60
Consumer | FICO not available | Personal, small business and other
Loans receivable
Loans, net of unearned income	2,522	755
Consumer | Total loans
Loans receivable
Loans, net of unearned income	$ 189,228	$ 208,464