ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Summary of Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance			$ 1,236
Provision (credited) charged to income			166	$ 181
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 1,219		1,219
Allowance for loan and lease losses
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	1,224	$ 1,224	1,236	1,216
Charge-offs	(128)	(113)	(261)	(239)
Recoveries	53	48	99	91
Net charge-offs	(75)	(65)	(162)	(148)
Provision (credited) charged to income	70	87	145	178
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,219	1,246	1,219	1,246
Allowance for loan and lease losses \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	653	633	663	596
Charge-offs	(24)	(7)	(48)	(20)
Recoveries	10	5	15	9
Net charge-offs	(14)	(2)	(33)	(11)
Provision (credited) charged to income	(25)	45	(16)	91
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	614	676	614	676
Allowance for loan and lease losses \| Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	571	591	573	620
Charge-offs	(104)	(106)	(213)	(219)
Recoveries	43	43	84	82
Net charge-offs	(61)	(63)	(129)	(137)
Provision (credited) charged to income	95	42	161	87
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	605	570	605	570
Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	93	58	72	58
Provision for unfunded lending commitments	0	3	21	3
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	93	61	93	61
Reserve for unfunded lending commitments \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	93	58	72	58
Provision for unfunded lending commitments	0	3	21	3
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	93	61	93	61
Reserve for unfunded lending commitments \| Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	0	0	0	0
Provision for unfunded lending commitments	0	0	0	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	0	0	0	0
Allowance for loan and lease losses and reserve for off-balance sheet activities, total
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,312	1,307	1,312	1,307
Allowance for loan and lease losses and reserve for off-balance sheet activities, total \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	707	737	707	737
Allowance for loan and lease losses and reserve for off-balance sheet activities, total \| Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 605	$ 570	$ 605	$ 570

Amount of provision (credit) for unfunded lending commitments recorded during the reporting period.

No definition available.

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- Definition

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount, after recoveries, of loans and leases that have been written-off.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
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