LOANS - Consumer Loans, Delinquencies and Non-Accrual Details (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) category	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) category	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Loans receivable
Number of loan categories | category	2		2
Loans, net of unearned income	$ 688,670		$ 688,670		$ 684,196
Loans at fair value	3,824		3,824		3,223
Consumer
Loans receivable
Loans, current	319,399		319,399		323,436
Loans, net of unearned income	325,995		325,995		330,487
Total non-accrual	2,228		2,228		2,226
90 days past due and accruing	2,284		$ 2,284		$ 2,548
Loans less than this number of days past due are considered current			30 days		30 days
Loans at fair value	20		$ 20		$ 20
Number of days past due, non-accrual status			60 days
Unearned income	713		$ 713		708
Loans sold and/or reclassified to held-for-sale	400	$ 1,900	2,300	$ 2,800
Consumer | Less than or equal to 80%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	49,117		49,117		51,844
Consumer | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	3,656		3,656		3,761
Consumer | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	500		500		587
Consumer | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	38,022		38,022		40,279
Consumer | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	74,759		74,759		77,963
Consumer | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	81,405		81,405		83,437
Consumer | Government-guaranteed
Loans receivable
Loans, past due	648		648		786
Consumer | 30 to 89 Days Past Due
Loans receivable
Loans, past due	3,155		3,155		3,264
Consumer | 90 days past due
Loans receivable
Loans, past due	2,793		2,793		3,001
Consumer | Residential first mortgages
Loans receivable
Loans at fair value	20		$ 20		$ 20
Number of days past due, non-accrual status			90 days		90 days
Consumer | Residential first mortgages | Less than or equal to 80%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	40,482		$ 40,482		$ 42,379
Consumer | Residential first mortgages | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	2,577		2,577		2,474
Consumer | Residential first mortgages | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	168		168		197
Consumer | Residential first mortgages | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	3,803		3,803		4,530
Consumer | Residential first mortgages | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	12,699		12,699		13,848
Consumer | Residential first mortgages | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	26,618		26,618		26,546
Consumer | Home equity loans | Less than or equal to 80%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	8,635		8,635		9,465
Consumer | Home equity loans | 80% but less than or equal to 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	1,079		1,079		1,287
Consumer | Home equity loans | Greater than 100%
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	332		332		390
Consumer | Home equity loans | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	2,172		2,172		2,438
Consumer | Home equity loans | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	3,920		3,920		4,296
Consumer | Home equity loans | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	3,994		3,994		4,471
Consumer | Credit cards | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	31,445		31,445		32,686
Consumer | Credit cards | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	57,173		57,173		58,722
Consumer | Credit cards | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	49,715		49,715		51,299
Consumer | Installment and other revolving | Less than 680
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	602		602		625
Consumer | Installment and other revolving | 680 to 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	967		967		1,097
Consumer | Installment and other revolving | Greater than 760
Financing Receivable
Purchased credit impaired in accordance with ASC 310-30	1,078		$ 1,078		1,121
Consumer | Commercial banking loans
Loans receivable
Number of days past due, non-accrual status			90 days
Consumer | In North America offices
Loans receivable
Loans, current	205,089		$ 205,089		211,251
Loans, net of unearned income	210,079		210,079		216,694
Total non-accrual	1,216		1,216		1,241
90 days past due and accruing	2,046		2,046		2,313
Consumer | In North America offices | Government-guaranteed
Loans receivable
Loans, past due	648		648		786
Consumer | In North America offices | 30 to 89 Days Past Due
Loans receivable
Loans, past due	2,231		2,231		2,331
Consumer | In North America offices | 90 days past due
Loans receivable
Loans, past due	2,111		2,111		2,326
Consumer | In North America offices | Residential first mortgages
Loans receivable
Loans, current	44,122		44,122		45,953
Loans, net of unearned income	45,474		45,474		47,412
Total non-accrual	582		582		583
90 days past due and accruing	407		407		549
Mortgage loans in process of foreclosure	100		100		100
Consumer | In North America offices | Residential first mortgages | Government-guaranteed
Loans receivable
Loans, past due	648		648		786
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due
Loans receivable
Loans, past due	480		480		420
Consumer | In North America offices | Residential first mortgages | 30 to 89 Days Past Due | Government-guaranteed
Loans receivable
Loans, past due	200		200		200
Consumer | In North America offices | Residential first mortgages | 90 days past due
Loans receivable
Loans, past due	224		224		253
Consumer | In North America offices | Residential first mortgages | 90 days past due | Government-guaranteed
Loans receivable
Loans, past due	400		400		600
Consumer | In North America offices | Home equity loans
Loans receivable
Loans, current	10,028		10,028		11,135
Loans, net of unearned income	10,404		10,404		11,543
Total non-accrual	476		476		527
90 days past due and accruing	0		0		0
Home equity loans in process of foreclosure	100		100		100
Consumer | In North America offices | Home equity loans | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In North America offices | Home equity loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	153		153		161
Consumer | In North America offices | Home equity loans | 90 days past due
Loans receivable
Loans, past due	223		223		247
Consumer | In North America offices | Credit cards
Loans receivable
Loans, current	137,091		137,091		141,106
Loans, net of unearned income	140,266		140,266		144,557
Total non-accrual	0		0		0
90 days past due and accruing	1,639		1,639		1,764
Consumer | In North America offices | Credit cards | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In North America offices | Credit cards | 30 to 89 Days Past Due
Loans receivable
Loans, past due	1,536		1,536		1,687
Consumer | In North America offices | Credit cards | 90 days past due
Loans receivable
Loans, past due	1,639		1,639		1,764
Consumer | In North America offices | Installment and other revolving
Loans receivable
Loans, current	3,193		3,193		3,395
Loans, net of unearned income	3,245		3,245		3,454
Total non-accrual	19		19		22
90 days past due and accruing	0		0		0
Consumer | In North America offices | Installment and other revolving | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In North America offices | Installment and other revolving | 30 to 89 Days Past Due
Loans receivable
Loans, past due	40		40		43
Consumer | In North America offices | Installment and other revolving | 90 days past due
Loans receivable
Loans, past due	12		12		16
Consumer | In North America offices | Commercial banking loans
Loans receivable
Loans, current	10,655		10,655		9,662
Loans, net of unearned income	10,690		10,690		9,728
Total non-accrual	139		139		109
90 days past due and accruing	0		0		0
Consumer | In North America offices | Commercial banking loans | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In North America offices | Commercial banking loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	22		22		20
Consumer | In North America offices | Commercial banking loans | 90 days past due
Loans receivable
Loans, past due	13		13		46
Consumer | In offices outside North America
Loans receivable
Loans, current	114,310		114,310		112,185
Loans, net of unearned income	115,916		115,916		113,793
Total non-accrual	1,012		1,012		985
90 days past due and accruing	238		238		235
Consumer | In offices outside North America | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In offices outside North America | 30 to 89 Days Past Due
Loans receivable
Loans, past due	924		924		933
Consumer | In offices outside North America | 90 days past due
Loans receivable
Loans, past due	682		682		675
Consumer | In offices outside North America | Residential first mortgages
Loans receivable
Loans, current	36,226		36,226		35,624
Loans, net of unearned income	36,580		36,580		35,972
Total non-accrual	405		405		383
90 days past due and accruing	0		0		0
Consumer | In offices outside North America | Residential first mortgages | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In offices outside North America | Residential first mortgages | 30 to 89 Days Past Due
Loans receivable
Loans, past due	207		207		203
Consumer | In offices outside North America | Residential first mortgages | 90 days past due
Loans receivable
Loans, past due	147		147		145
Consumer | In offices outside North America | Credit cards
Loans receivable
Loans, current	24,188		24,188		24,131
Loans, net of unearned income	24,975		24,975		24,926
Total non-accrual	302		302		312
90 days past due and accruing	238		238		235
Consumer | In offices outside North America | Credit cards | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In offices outside North America | Credit cards | 30 to 89 Days Past Due
Loans receivable
Loans, past due	416		416		425
Consumer | In offices outside North America | Credit cards | 90 days past due
Loans receivable
Loans, past due	371		371		370
Consumer | In offices outside North America | Installment and other revolving
Loans receivable
Loans, current	26,970		26,970		25,773
Loans, net of unearned income	27,321		27,321		26,134
Total non-accrual	146		146		152
90 days past due and accruing	0		0		0
Consumer | In offices outside North America | Installment and other revolving | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In offices outside North America | Installment and other revolving | 30 to 89 Days Past Due
Loans receivable
Loans, past due	241		241		254
Consumer | In offices outside North America | Installment and other revolving | 90 days past due
Loans receivable
Loans, past due	110		110		107
Consumer | In offices outside North America | Commercial banking loans
Loans receivable
Loans, current	26,926		26,926		26,657
Loans, net of unearned income	27,040		27,040		26,761
Total non-accrual	159		159		138
90 days past due and accruing	0		0		0
Consumer | In offices outside North America | Commercial banking loans | Government-guaranteed
Loans receivable
Loans, past due	0		0		0
Consumer | In offices outside North America | Commercial banking loans | 30 to 89 Days Past Due
Loans receivable
Loans, past due	60		60		51
Consumer | In offices outside North America | Commercial banking loans | 90 days past due
Loans receivable
Loans, past due	$ 54		$ 54		$ 53