LOANS - Consumer Loans, Delinquencies and Non-Accrual Details (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) category	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Financing Receivable, Past Due [Line Items]
Number of loan categories | category	2
Total loans	$ 659,669		$ 667,767
Loans held at fair value	5,732		6,082
Consumer
Financing Receivable, Past Due [Line Items]
Total loans	350,328		376,534
Non-accrual loans for which there is no ACLL	140		200
Non-accrual loans for which there is an ACLL	1,377		1,626
Total non-accrual	1,517		1,826
90 days  past due and accruing	1,240		1,335
Loans held at fair value	10		12
Unearned income	591		629
Loans sold and/or reclassified to held-for-sale	7	$ 96
Consumer | Current
Financing Receivable, Past Due [Line Items]
Total loans	346,420		371,731
Consumer | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	1,713		2,480
Consumer | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	1,815		1,891
Consumer | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	380		432
Consumer | In North America offices
Financing Receivable, Past Due [Line Items]
Total loans	261,183		263,687
Non-accrual loans for which there is no ACLL	140		200
Non-accrual loans for which there is an ACLL	774		850
Total non-accrual	914		1,050
90 days  past due and accruing	1,182		1,183
Consumer | In North America offices | Current
Financing Receivable, Past Due [Line Items]
Total loans	257,856		259,807
Consumer | In North America offices | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	1,429		1,978
Consumer | In North America offices | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	1,518		1,470
Consumer | In North America offices | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	380		432
Consumer | In offices outside North America
Financing Receivable, Past Due [Line Items]
Total loans	89,145		112,847
Non-accrual loans for which there is no ACLL	0		0
Non-accrual loans for which there is an ACLL	603		776
Total non-accrual	603		776
90 days  past due and accruing	58		152
Consumer | In offices outside North America | Current
Financing Receivable, Past Due [Line Items]
Total loans	88,564		111,924
Consumer | In offices outside North America | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	284		502
Consumer | In offices outside North America | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	297		421
Consumer | In offices outside North America | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	0		0
Consumer | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total loans	84,569		83,361
Loans held at fair value	10		12
Consumer | Residential mortgages | In North America offices
Financing Receivable, Past Due [Line Items]
Total loans	84,569		83,361
Non-accrual loans for which there is no ACLL	82		134
Non-accrual loans for which there is an ACLL	506		559
Total non-accrual	588		693
90 days  past due and accruing	240		282
Mortgage loans in process of foreclosure	100		100
Consumer | Residential mortgages | In North America offices | Current
Financing Receivable, Past Due [Line Items]
Total loans	83,520		82,234
Consumer | Residential mortgages | In North America offices | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	329		454
Consumer | Residential mortgages | In North America offices | 30 to 89 days past due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	100		100
Consumer | Residential mortgages | In North America offices | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	376		279
Consumer | Residential mortgages | In North America offices | 90 days or more past due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	300		300
Consumer | Residential mortgages | In North America offices | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	344		394
Consumer | Residential mortgages | In offices outside North America
Financing Receivable, Past Due [Line Items]
Total loans	29,017		37,889
Non-accrual loans for which there is no ACLL	0		0
Non-accrual loans for which there is an ACLL	326		409
Total non-accrual	326		409
90 days  past due and accruing	10		10
Mortgage loans in process of foreclosure	0
Consumer | Residential mortgages | In offices outside North America | Current
Financing Receivable, Past Due [Line Items]
Total loans	28,854		37,566
Consumer | Residential mortgages | In offices outside North America | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	67		165
Consumer | Residential mortgages | In offices outside North America | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	96		158
Consumer | Residential mortgages | In offices outside North America | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	0		0
Consumer | Home equity loans
Financing Receivable, Past Due [Line Items]
Total loans	5,328		5,745
Consumer | Home equity loans | In North America offices
Financing Receivable, Past Due [Line Items]
Total loans	5,328		5,745
Non-accrual loans for which there is no ACLL	56		64
Non-accrual loans for which there is an ACLL	198		221
Total non-accrual	254		285
90 days  past due and accruing	0		0
Home equity loans in process of foreclosure	100		100
Consumer | Home equity loans | In North America offices | Current
Financing Receivable, Past Due [Line Items]
Total loans	5,127		5,546
Consumer | Home equity loans | In North America offices | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	36		43
Consumer | Home equity loans | In North America offices | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	165		156
Consumer | Home equity loans | In North America offices | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	0		0
Consumer | Home equity loans | In offices outside North America
Financing Receivable, Past Due [Line Items]
Home equity loans in process of foreclosure	0
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Total loans	129,482		133,351
Consumer | Credit cards | In North America offices
Financing Receivable, Past Due [Line Items]
Total loans	129,989		133,868
Non-accrual loans for which there is no ACLL	0		0
Non-accrual loans for which there is an ACLL	0		0
Total non-accrual	0		0
90 days  past due and accruing	910		871
Consumer | Credit cards | In North America offices | Current
Financing Receivable, Past Due [Line Items]
Total loans	128,091		132,050
Consumer | Credit cards | In North America offices | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	988		947
Consumer | Credit cards | In North America offices | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	910		871
Consumer | Credit cards | In North America offices | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	0		0
Consumer | Credit cards | In offices outside North America
Financing Receivable, Past Due [Line Items]
Total loans	11,546		17,808
Non-accrual loans for which there is no ACLL	0		0
Non-accrual loans for which there is an ACLL	98		140
Total non-accrual	98		140
90 days  past due and accruing	48		120
Consumer | Credit cards | In offices outside North America | Current
Financing Receivable, Past Due [Line Items]
Total loans	11,309		17,428
Consumer | Credit cards | In offices outside North America | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	116		192
Consumer | Credit cards | In offices outside North America | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	121		188
Consumer | Credit cards | In offices outside North America | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	0		0
Consumer | Personal, small business and other
Financing Receivable, Past Due [Line Items]
Total loans	40,359		39,806
Consumer | Personal, small business and other | In North America offices
Financing Receivable, Past Due [Line Items]
Total loans	41,297		40,713
Non-accrual loans for which there is no ACLL	2		2
Non-accrual loans for which there is an ACLL	70		70
Total non-accrual	72		72
90 days  past due and accruing	32		30
Consumer | Personal, small business and other | In North America offices | Current
Financing Receivable, Past Due [Line Items]
Total loans	41,118		39,977
Consumer | Personal, small business and other | In North America offices | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	76		534
Consumer | Personal, small business and other | In North America offices | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	67		164
Consumer | Personal, small business and other | In North America offices | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	36		38
Consumer | Personal, small business and other | In offices outside North America
Financing Receivable, Past Due [Line Items]
Total loans	48,582		57,150
Non-accrual loans for which there is no ACLL	0		0
Non-accrual loans for which there is an ACLL	179		227
Total non-accrual	179		227
90 days  past due and accruing	0		22
Consumer | Personal, small business and other | In offices outside North America | Current
Financing Receivable, Past Due [Line Items]
Total loans	48,401		56,930
Consumer | Personal, small business and other | In offices outside North America | 30 to 89 days past due
Financing Receivable, Past Due [Line Items]
Total loans	101		145
Consumer | Personal, small business and other | In offices outside North America | 90 days or more past due
Financing Receivable, Past Due [Line Items]
Total loans	80		75
Consumer | Personal, small business and other | In offices outside North America | Past Due | Government-guaranteed
Financing Receivable, Past Due [Line Items]
Total loans	$ 0		$ 0