ALLOWANCE FOR CREDIT LOSSES - Allowance for Loan Losses Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Allowance for credit losses
Allowance for loan losses at beginning of period	$ 12,025	$ 12,304	$ 12,060	$ 12,626
Gross credit losses	(2,120)	(1,948)	(6,394)	(6,139)
Gross recoveries	343	423	1,198	1,274
Net credit losses (NCLs)	(1,777)	(1,525)	(5,196)	(4,865)
Net credit losses (NCLs)	1,777	1,525	5,196	4,865
Net reserve builds (releases)	419	258	466	210
Net specific reserve releases	(50)	(37)	(175)	(53)
Total provision for loan losses	2,146	1,746	5,487	5,022
Other, net	(28)	(86)	15	(344)
Allowance for loan losses at end of period	12,366	12,439	12,366	12,439
Allowance for credit losses on unfunded lending commitments
Allowance for credit losses on unfunded lending commitments at beginning of period	1,406	1,432	1,418	1,402
Release for unfunded lending commitments	(175)	(45)	(190)	(4)
Other, net	1	1	4	(10)
Allowance for credit losses on unfunded lending commitments at end of period	1,232	1,388	1,232	1,388
Total allowance for loans, leases and unfunded lending commitments	13,598	13,827	13,598	13,827
Sales or transfers of various consumer loan portfolios to held-for-sale
Other, net	(28)	(86)	15	(344)
Consumer
Allowance for credit losses
Allowance for loan losses at beginning of period	9,515	9,432	9,358	9,835
Gross credit losses	(2,071)	(1,885)	(6,146)	(5,694)
Gross recoveries	337	400	1,107	1,222
Net credit losses (NCLs)	(1,734)	(1,485)	(5,039)	(4,472)
Net credit losses (NCLs)	1,734	1,485	5,039	4,472
Net reserve builds (releases)	479	368	696	332
Net specific reserve releases	(71)	(36)	(157)	(142)
Other, net	(31)	(91)	(5)	(352)
Allowance for loan losses at end of period	9,892	9,673	9,892	9,673
Sales or transfers of various consumer loan portfolios to held-for-sale
Transfer of real estate loan portfolios	(28)	(50)	(84)	(103)
Transfer of other loan portfolios	(6)	(8)	(130)	(204)
Sales or transfers of various consumer loan portfolios to held-for-sale	(34)	(58)	(214)	(307)
FX translation, consumer	7	(46)	221	(58)
Other, net	(31)	(91)	(5)	(352)
Corporate
Allowance for credit losses
Allowance for loan losses at beginning of period	2,510	2,872	2,702	2,791
Gross credit losses	(49)	(63)	(248)	(445)
Gross recoveries	6	23	91	52
Net credit losses (NCLs)	(43)	(40)	(157)	(393)
Net credit losses (NCLs)	43	40	157	393
Net reserve builds (releases)	(60)	(110)	(230)	(122)
Net specific reserve releases	21	(1)	(18)	89
Other, net	3	5	20	8
Allowance for loan losses at end of period	2,474	2,766	2,474	2,766
Sales or transfers of various consumer loan portfolios to held-for-sale
Other	(1)	18	8	21
Other, net	$ 3	$ 5	$ 20	$ 8