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	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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 charged to income			238	$ 267
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 1,224		1,224
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	1,219	$ 1,246	1,236	1,216
Charge-offs	(120)	(145)	(381)	(384)
Recoveries	55	62	154	153
Net charge-offs	(65)	(83)	(227)	(231)
Provision charged to income	70	77	215	255
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,224	1,240	1,224	1,240
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	61	72	58
Provision for unfunded lending commitments	2	9	23	12
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	95	70	95	70
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	1,319	1,310	1,319	1,310
Commercial \| 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	614	676	663	596
Charge-offs	(12)	(33)	(60)	(53)
Recoveries	12	14	27	23
Net charge-offs	0	(19)	(33)	(30)
Provision charged to income	24	(2)	8	89
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	638	655	638	655
Commercial \| 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	61	72	58
Provision for unfunded lending commitments	2	9	23	12
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	95	70	95	70
Commercial \| 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	733	725	733	725
Retail \| 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	605	570	573	620
Charge-offs	(108)	(112)	(321)	(331)
Recoveries	43	48	127	130
Net charge-offs	(65)	(64)	(194)	(201)
Provision charged to income	46	79	207	166
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	586	585	586	585
Retail \| 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	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
Retail \| 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	$ 586	$ 585	$ 586	$ 585

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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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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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
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