ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,060	$ 12,626	$ 15,994
Gross credit losses	(8,673)	(8,222)	(9,041)
Gross recoveries	1,597	1,661	1,739
Net credit losses (NCLs)	(7,076)	(6,561)	(7,302)
NCLs	7,076	6,561	7,302
Net reserve builds (releases)	544	340	139
Net specific reserve releases	(117)	(152)	(333)
Total provision for loan losses	7,503	6,749	7,108
Other	(132)	(754)	(3,174)
Allowance for loan losses at the end of year	12,355	12,060	12,626
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,418	1,402	1,063
Provision (release) for unfunded lending commitments	(161)	29	74
Other, net	1	(13)	265
Allowance for credit losses on unfunded lending commitments at end of period	1,258	1,418	1,402
Total allowance for loans, leases and unfunded lending commitments	13,613	13,478	14,028
Allowance for loan losses included in other transferred to allowance for unfunded lending commitments			271
Sales or transfers of various consumer loan portfolios to held-for-sale
Other	(132)	(754)	(3,174)
Consumer
Sales or transfers of various consumer loan portfolios to held-for-sale
Transfer of real estate loan portfolios	(106)	(106)	(1,462)
Transfer of other loan portfolios	(155)	(468)	(948)
Sales or transfers of various consumer loan portfolios to held-for-sale	(261)	(574)	(2,410)
FX translation, consumer	115	(199)	(474)
Corporate
Allowance for credit losses
Other	14	19	(290)
Sales or transfers of various consumer loan portfolios to held-for-sale
Other	$ 14	$ 19	$ (290)