ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Summary of Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	$ 1,216
Provision charged to income	369	$ 302	$ 319
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,236	1,216
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	1,216	1,195	1,221
Charge-offs	(536)	(480)	(493)
Recoveries	201	196	170
Net charge-offs	(335)	(284)	(323)
Provision charged to income	355	305	297
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,236	1,216	1,195
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	596	544	498
Charge-offs	(79)	(36)	(43)
Recoveries	33	49	58
Net charge-offs	(46)	13	15
Provision charged to income	113	39	31
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	663	596	544
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	620	651	723
Charge-offs	(457)	(444)	(450)
Recoveries	168	147	112
Net charge-offs	(289)	(297)	(338)
Provision charged to income	242	266	266
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	573	620	651
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	58	61	39
Provision (credit) for unfunded lending commitments	14	(3)	22
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	72	58	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	58	61	39
Provision (credit) for unfunded lending commitments	14	(3)	22
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	72	58	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
Provision (credit) for unfunded lending commitments	0	0	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	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, Beginning balance	1,274	1,256
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,308	1,274	1,256
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, Beginning balance	654	605
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	735	654	605
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, Beginning balance	620	651
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 573	$ 620	$ 651

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.

+ References

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- Definition

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

+ References

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- Definition

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
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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.

+ References

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