LOANS - Consumer Troubled Debt Restructurings (Details) - Consumer $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan
Loans receivable
Period within which default occurred post-modification			1 year
Number of days past due, non-accrual status			60 days
In North America offices
Loans receivable
Number of loans modified | loan	34,227	50,248	131,064	169,937
Post-modification recorded investment	$ 209	$ 320	$ 823	$ 964
TDR loans in payment default	$ 72	$ 101	$ 250	$ 325
In North America offices | Residential first mortgages
Loans receivable
Number of loans modified | loan	281	237	942	812
Post-modification recorded investment	$ 48	$ 42	$ 163	$ 137
Average interest rate reduction	1.00%	0.00%	0.00%	0.00%
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 4	$ 2	$ 11	$ 10
TDR loans in payment default	10	24	43	59
In North America offices | Residential first mortgages | New OCC guidance
Loans receivable
Post-modification recorded investment for borrowers that have gone through Chapter 7 bankruptcy	$ 2	$ 1	$ 4	$ 7
In North America offices | Home equity loans
Loans receivable
Number of loans modified | loan	31	62	138	227
Post-modification recorded investment	$ 1	$ 5	$ 9	$ 22
Average interest rate reduction	1.00%	0.00%	0.00%	1.00%
TDR loans in payment default	$ 1	$ 6	$ 8	$ 12
In North America offices | Credit cards
Loans receivable
Number of loans modified | loan	33,746	48,909	129,129	167,082
Post-modification recorded investment	$ 159	$ 261	$ 639	$ 786
Average interest rate reduction	18.00%	17.00%	17.00%	13.00%
TDR loans in payment default	$ 60	$ 70	$ 196	$ 251
In North America offices | Personal, small business and other
Loans receivable
Number of loans modified | loan	169	1,040	855	1,816
Post-modification recorded investment	$ 1	$ 12	$ 12	$ 19
Average interest rate reduction	4.00%	6.00%	3.00%	4.00%
TDR loans in payment default	$ 1	$ 1	$ 3	$ 3
In offices outside North America
Loans receivable
Number of loans modified | loan	23,869	38,495	82,079	99,202
Post-modification recorded investment	$ 142	$ 249	$ 503	$ 603
TDR loans in payment default	$ 74	$ 73	$ 251	$ 190
In offices outside North America | Residential first mortgages
Loans receivable
Number of loans modified | loan	451	696	1,448	1,874
Post-modification recorded investment	$ 22	$ 21	$ 74	$ 80
Average interest rate reduction	0.00%	1.00%	0.00%	4.00%
TDR loans in payment default	$ 9	$ 6	$ 31	$ 17
In offices outside North America | Credit cards
Loans receivable
Number of loans modified | loan	16,082	25,147	58,978	65,738
Post-modification recorded investment	$ 71	$ 122	$ 267	$ 289
Average interest rate reduction	15.00%	14.00%	14.00%	16.00%
TDR loans in payment default	$ 36	$ 47	$ 133	$ 118
In offices outside North America | Personal, small business and other
Loans receivable
Number of loans modified | loan	7,336	12,652	21,653	31,590
Post-modification recorded investment	$ 49	$ 106	$ 162	$ 234
Average interest rate reduction	9.00%	10.00%	9.00%	10.00%
TDR loans in payment default	$ 29	$ 20	$ 87	$ 55
Deferred principal | In North America offices
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Deferred principal | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Contingent principal forgiveness | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Home equity loans
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Credit cards
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In North America offices | Personal, small business and other
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In offices outside North America
Loans receivable
Post-modification recorded investment	4	4	15	13
Principal forgiveness | In offices outside North America | Residential first mortgages
Loans receivable
Post-modification recorded investment	0	0	0	0
Principal forgiveness | In offices outside North America | Credit cards
Loans receivable
Post-modification recorded investment	2	2	10	7
Principal forgiveness | In offices outside North America | Personal, small business and other
Loans receivable
Post-modification recorded investment	$ 2	$ 2	$ 5	$ 6