ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,126	$ 12,025	$ 12,355	$ 12,060
Gross credit losses	(2,094)	(2,120)	(6,499)	(6,394)
Gross recoveries	338	343	1,172	1,198
Net credit losses (NCLs)	(1,756)	(1,777)	(5,327)	(5,196)
Net reserve builds (releases)	169	419	302	466
Net specific reserve builds (releases)	(19)	(50)	(125)	(175)
Total provision for loan losses	1,906	2,146	5,504	5,487
Other, net	60	(28)	(196)	15
Allowance for loan losses at end of period	12,336	12,366	12,336	12,366
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,278	1,406	1,258	1,418
Provision (release) for unfunded lending commitments	42	(175)	66	(190)
Other, net	1	1	(3)	4
Allowance for credit losses on unfunded lending commitments at end of period	1,321	1,232	1,321	1,232
Total allowance for loans, leases and unfunded lending commitments	13,657	13,598	13,657	13,598
Sales or transfers of various consumer loan portfolios to HFS
Other, net	60	(28)	(196)	15
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	9,796	9,515	9,869	9,358
Gross credit losses	(2,058)	(2,071)	(6,304)	(6,146)
Gross recoveries	332	337	1,101	1,107
Net credit losses (NCLs)	(1,726)	(1,734)	(5,203)	(5,039)
Net reserve builds (releases)	135	479	317	696
Net specific reserve builds (releases)	8	(71)	(6)	(157)
Other, net	58	(31)	(183)	(5)
Allowance for loan losses at end of period	9,997	9,892	9,997	9,892
Sales or transfers of various consumer loan portfolios to HFS
Transfer of real estate loan portfolios	(2)	(28)	(88)	(84)
Transfer of other loan portfolios	(3)	(6)	(109)	(130)
Sales or transfers of various consumer loan portfolios to HFS	(5)	(34)	(197)	(214)
FX translation, consumer	62	7	16	221
Other, net	58	(31)	(183)	(5)
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,330	2,510	2,486	2,702
Gross credit losses	(36)	(49)	(195)	(248)
Gross recoveries	6	6	71	91
Net credit losses (NCLs)	(30)	(43)	(124)	(157)
Net reserve builds (releases)	34	(60)	(15)	(230)
Net specific reserve builds (releases)	(27)	21	(119)	(18)
Other, net	2	3	(13)	20
Allowance for loan losses at end of period	2,339	2,474	2,339	2,474
Sales or transfers of various consumer loan portfolios to HFS
Other	3	(1)	(15)	8
Other, net	$ 2	$ 3	$ (13)	$ 20