ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,466	$ 12,126	$ 12,315	$ 12,355
Gross credit losses	(2,281)	(2,094)	(6,980)	(6,499)
Gross recoveries	368	338	1,156	1,172
Net credit losses (NCLs)	(1,913)	(1,756)	(5,824)	(5,327)
Net reserve builds (releases)	132	169	252	302
Net specific reserve builds (releases)	17	(19)	19	(125)
Total provision for loan losses	2,062	1,906	6,095	5,504
Other, net	(85)	60	(56)	(196)
Allowance for loan losses at end of period	12,530	12,336	12,530	12,336
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,376	1,278	1,367	1,258
Provision (release) for unfunded lending commitments	9	42	18	66
Other, net	0	1	0	(3)
Allowance for credit losses on unfunded lending commitments at end of period	1,385	1,321	1,385	1,321
Total allowance for loans, leases and unfunded lending commitments	13,915	13,657	13,915	13,657
Sales or transfers of various consumer loan portfolios to HFS
Other, net	(85)	60	(56)	(196)
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	10,113	9,796	9,950	9,869
Gross credit losses	(2,174)	(2,058)	(6,717)	(6,304)
Gross recoveries	350	332	1,108	1,101
Net credit losses (NCLs)	(1,824)	(1,726)	(5,609)	(5,203)
Net reserve builds (releases)	121	135	196	317
Net specific reserve builds (releases)	34	8	88	(6)
Other, net	(69)	58	(35)	(183)
Allowance for loan losses at end of period	10,199	9,997	10,199	9,997
Sales or transfers of various consumer loan portfolios to HFS
Transfer of real estate loan portfolios	(5)	(2)	(9)	(88)
Transfer of other loan portfolios	0	(3)	0	(109)
Sales or transfers of various consumer loan portfolios to HFS	(5)	(5)	(9)	(197)
FX translation, consumer	(65)	62	(26)	16
Other, net	(69)	58	(35)	(183)
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,353	2,330	2,365	2,486
Gross credit losses	(107)	(36)	(263)	(195)
Gross recoveries	18	6	48	71
Net credit losses (NCLs)	(89)	(30)	(215)	(124)
Net reserve builds (releases)	11	34	56	(15)
Net specific reserve builds (releases)	(17)	(27)	(69)	(119)
Other, net	(16)	2	(21)	(13)
Allowance for loan losses at end of period	2,331	2,339	2,331	2,339
Sales or transfers of various consumer loan portfolios to HFS
Other	(15)	3	(21)	(15)
Other, net	$ (16)	$ 2	$ (21)	$ (13)