ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,354	$ 12,030	$ 12,355	$ 12,060
Gross credit losses	(2,109)	(2,130)	(4,405)	(4,274)
Gross recoveries	405	420	834	855
Net credit losses (NCLs)	(1,704)	(1,710)	(3,571)	(3,419)
Replenishment of net charge-offs	1,704	1,710	3,571	3,419
Net reserve builds (releases)	31	67	133	47
Net specific reserve releases	60	(111)	(106)	(125)
Total provision for loan losses	1,795	1,666	3,598	3,341
Other, net	(319)	39	(256)	43
Allowance for loan losses at end of period	12,126	12,025	12,126	12,025
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,290	1,377	1,258	1,418
Provision (release) for unfunded lending commitments	(4)	28	24	(15)
Other, net	(8)	1	(4)	3
Allowance for credit losses on unfunded lending commitments at end of period	1,278	1,406	1,278	1,406
Total allowance for loans, leases and unfunded lending commitments	13,404	13,431	13,404	13,431
Sales or transfers of various consumer loan portfolios to HFS
Other, net	(319)	39	(256)	43
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	10,039	9,495	9,869	9,358
Gross credit losses	(2,089)	(2,034)	(4,246)	(4,075)
Gross recoveries	383	401	769	770
Net credit losses (NCLs)	(1,706)	(1,633)	(3,477)	(3,305)
Replenishment of net charge-offs	1,706	1,633	3,477	3,305
Net reserve builds (releases)	61	71	182	217
Net specific reserve releases	(3)	(84)	(14)	(86)
Other, net	(301)	33	(241)	26
Allowance for loan losses at end of period	9,796	9,515	9,796	9,515
Sales or transfers of various consumer loan portfolios to HFS
Transfer of real estate loan portfolios	(33)	(19)	(86)	(56)
Transfer of other loan portfolios	(104)	0	(106)	(124)
Sales or transfers of various consumer loan portfolios to HFS	(137)	(19)	(192)	(180)
FX translation, consumer	(164)	50	(46)	214
Other, net	(301)	33	(241)	26
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,315	2,535	2,486	2,702
Gross credit losses	(20)	(96)	(159)	(199)
Gross recoveries	22	19	65	85
Net credit losses (NCLs)	2	(77)	(94)	(114)
Replenishment of net charge-offs	(2)	77	94	114
Net reserve builds (releases)	(30)	(4)	(49)	(170)
Net specific reserve releases	63	(27)	(92)	(39)
Other, net	(18)	6	(15)	17
Allowance for loan losses at end of period	2,330	2,510	2,330	2,510
Sales or transfers of various consumer loan portfolios to HFS
Other	(18)	8	(18)	9
Other, net	$ (18)	$ 6	$ (15)	$ 17