LOANS - Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 659,669	$ 667,767
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	350,328	376,534
Consumer | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	84,569	83,361
Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	129,482	133,351
Consumer | Credit cards | CANADA
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	507	517
Consumer | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	5,328	5,745
Consumer | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	40,359	39,806
Consumer | Personal, small business and other | CANADA
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	938	907
Consumer | Less than or equal to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	83,724	83,339
Consumer | Less than or equal to 80% | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	3,491	18,107
One year prior to current fiscal year	18,705	18,715
Two years prior to current fiscal year	17,885	10,047
Three years prior to current fiscal year	9,435	4,117
Four years prior to current fiscal year	3,949	4,804
Prior	25,225	22,161
Total loans, net of unearned income	78,690	77,951
Consumer | Less than or equal to 80% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,434	2,637
Consumer | Less than or equal to 80% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,600	2,751
Consumer | Less than or equal to 80% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	5,034	5,388
Consumer | Greater than 80% but less than or equal to 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	4,299	3,903
Consumer | Greater than 80% but less than or equal to 100% | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	853	2,723
One year prior to current fiscal year	2,359	446
Two years prior to current fiscal year	426	269
Three years prior to current fiscal year	231	136
Four years prior to current fiscal year	124	103
Prior	224	128
Total loans, net of unearned income	4,217	3,805
Consumer | Greater than 80% but less than or equal to 100% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	37	46
Consumer | Greater than 80% but less than or equal to 100% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	45	52
Consumer | Greater than 80% but less than or equal to 100% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	82	98
Consumer | Greater than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	185	193
Consumer | Greater than 100% | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	3	34
One year prior to current fiscal year	35	0
Two years prior to current fiscal year	0	29
Three years prior to current fiscal year	29	11
Four years prior to current fiscal year	11	4
Prior	15	14
Total loans, net of unearned income	93	92
Consumer | Greater than 100% | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	59	69
Consumer | Greater than 100% | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	33	32
Consumer | Greater than 100% | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	92	101
Consumer | LTV not available
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,689	1,671
Consumer | LTV not available | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,569	1,513
Consumer | LTV not available | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	120	158
Consumer | Total
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	89,897	89,106
Consumer | Less than 680
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	29,063	28,598
Consumer | Less than 680 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	107	626
One year prior to current fiscal year	757	508
Two years prior to current fiscal year	494	373
Three years prior to current fiscal year	342	394
Four years prior to current fiscal year	388	343
Prior	2,366	2,053
Total loans, net of unearned income	4,454	4,297
Consumer | Less than 680 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	23,462	23,115
Consumer | Less than 680 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	247	263
Consumer | Less than 680 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	593	639
Consumer | Less than 680 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	840	902
Consumer | Less than 680 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	8	59
One year prior to current fiscal year	92	22
Two years prior to current fiscal year	21	42
Three years prior to current fiscal year	36	34
Four years prior to current fiscal year	26	7
Prior	124	120
Total loans, net of unearned income	307	284
Consumer | 680 to 760
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	77,215	79,581
Consumer | 680 to 760 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,288	6,729
One year prior to current fiscal year	6,249	5,102
Two years prior to current fiscal year	4,776	3,074
Three years prior to current fiscal year	2,670	1,180
Four years prior to current fiscal year	1,046	1,455
Prior	6,958	6,540
Total loans, net of unearned income	22,987	24,080
Consumer | 680 to 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	51,745	52,907
Consumer | 680 to 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	949	1,030
Consumer | 680 to 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	963	1,047
Consumer | 680 to 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,912	2,077
Consumer | 680 to 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	34	201
One year prior to current fiscal year	251	41
Two years prior to current fiscal year	34	53
Three years prior to current fiscal year	44	35
Four years prior to current fiscal year	27	8
Prior	181	179
Total loans, net of unearned income	571	517
Consumer | Greater than 760
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	105,830	106,515
Consumer | Greater than 760 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,890	12,349
One year prior to current fiscal year	12,930	12,153
Two years prior to current fiscal year	11,663	6,167
Three years prior to current fiscal year	5,959	2,216
Four years prior to current fiscal year	2,185	2,568
Prior	14,528	12,586
Total loans, net of unearned income	50,155	48,039
Consumer | Greater than 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	52,433	55,137
Consumer | Greater than 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,426	1,539
Consumer | Greater than 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,104	1,160
Consumer | Greater than 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,530	2,699
Consumer | Greater than 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	59	319
One year prior to current fiscal year	376	64
Two years prior to current fiscal year	52	68
Three years prior to current fiscal year	55	37
Four years prior to current fiscal year	28	9
Prior	142	143
Total loans, net of unearned income	712	640
Consumer | FICO not available
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	47,630	47,569
Consumer | FICO not available | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	6,973	6,945
Consumer | FICO not available | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,842	2,192
Consumer | FICO not available | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	46	67
Consumer | FICO not available | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	38,769	38,365
Consumer | Total loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 259,738	$ 262,263