ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,355	$ 12,060
Gross credit losses	(2,296)	(2,144)
Gross recoveries	429	435
Net credit losses (NCLs)	(1,867)	(1,709)
Net credit losses (NCLs)	1,867	1,709
Net reserve builds (releases)	102	(20)
Net specific reserve releases	(166)	(14)
Total provision for loan losses	1,803	1,675
Other, net	63	4
Allowance for loan losses at end of period	12,354	12,030
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,258	1,418
Provision (release) for unfunded lending commitments	28	(43)
Other, net	4	2
Allowance for credit losses on unfunded lending commitments at end of period	1,290	1,377
Total allowance for loans, leases and unfunded lending commitments	13,644	13,407
Sales or transfers of various consumer loan portfolios to HFS
Other, net	63	4
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	9,869	9,358
Gross credit losses	(2,157)	(2,041)
Gross recoveries	386	369
Net credit losses (NCLs)	(1,771)	(1,672)
Net credit losses (NCLs)	1,771	1,672
Net reserve builds (releases)	121	146
Net specific reserve releases	(11)	(2)
Other, net	60	(7)
Allowance for loan losses at end of period	10,039	9,495
Sales or transfers of various consumer loan portfolios to HFS
Transfer of real estate loan portfolios	(53)	(37)
Transfer of other loan portfolios	(2)	(124)
Sales or transfers of various consumer loan portfolios to HFS	(55)	(161)
FX translation, consumer	118	164
Other, net	60	(7)
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,486	2,702
Gross credit losses	(139)	(103)
Gross recoveries	43	66
Net credit losses (NCLs)	(96)	(37)
Net credit losses (NCLs)	96	37
Net reserve builds (releases)	(19)	(166)
Net specific reserve releases	(155)	(12)
Other, net	3	11
Allowance for loan losses at end of period	2,315	2,535
Sales or transfers of various consumer loan portfolios to HFS
Other	0	1
Other, net	$ 3	$ 11