ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,329	$ 12,354	$ 12,315	$ 12,355
Gross credit losses	(2,354)	(2,109)	(4,699)	(4,405)
Gross recoveries	391	405	788	834
Net credit losses (NCLs)	(1,963)	(1,704)	(3,911)	(3,571)
Net reserve builds (releases)	53	31	120	133
Net specific reserve builds (releases)	73	60	2	(106)
Total provision for loan losses	2,089	1,795	4,033	3,598
Other, net	11	(319)	29	(256)
Allowance for loan losses at end of period	12,466	12,126	12,466	12,126
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,391	1,290	1,367	1,258
Provision (release) for unfunded lending commitments	(15)	(4)	9	24
Other, net	0	(8)	0	(4)
Allowance for credit losses on unfunded lending commitments at end of period	1,376	1,278	1,376	1,278
Total allowance for loans, leases and unfunded lending commitments	13,842	13,404	13,842	13,404
Sales or transfers of various consumer loan portfolios to HFS
Other, net	11	(319)	29	(256)
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	10,026	10,039	9,950	9,869
Gross credit losses	(2,271)	(2,089)	(4,543)	(4,246)
Gross recoveries	378	383	758	769
Net credit losses (NCLs)	(1,893)	(1,706)	(3,785)	(3,477)
Net reserve builds (releases)	15	61	75	182
Net specific reserve builds (releases)	64	(3)	54	(14)
Other, net	8	(301)	34	(241)
Allowance for loan losses at end of period	10,113	9,796	10,113	9,796
Sales or transfers of various consumer loan portfolios to HFS
Transfer of real estate loan portfolios	(4)	(33)	(4)	(86)
Transfer of other loan portfolios	0	(104)	0	(106)
Sales or transfers of various consumer loan portfolios to HFS	(4)	(137)	(4)	(192)
FX translation, consumer	13	(164)	39	(46)
Other, net	8	(301)	34	(241)
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,303	2,315	2,365	2,486
Gross credit losses	(83)	(20)	(156)	(159)
Gross recoveries	13	22	30	65
Net credit losses (NCLs)	(70)	2	(126)	(94)
Net reserve builds (releases)	38	(30)	45	(49)
Net specific reserve builds (releases)	9	63	(52)	(92)
Other, net	3	(18)	(5)	(15)
Allowance for loan losses at end of period	2,353	2,330	2,353	2,330
Sales or transfers of various consumer loan portfolios to HFS
Other	2	(18)	(6)	(18)
Other, net	$ 3	$ (18)	$ (5)	$ (15)