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, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	$ 1,195
Provision charged to income	302	$ 319	$ 479
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,216	1,195
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	1,195	1,221	1,255
Charge-offs	(480)	(493)	(703)
Recoveries	196	170	202
Net recoveries (charge-offs)	(284)	(323)	(501)
Sales/Other			(13)
Provision charged to income	305	297	480
Transfer of unallocated reserve to qualitative reserve			0
Loss emergence period change			0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,216	1,195	1,221
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	544	498	509
Charge-offs	(36)	(43)	(108)
Recoveries	49	58	87
Net recoveries (charge-offs)	13	15	(21)
Sales/Other			(6)
Provision charged to income	39	31	(19)
Transfer of unallocated reserve to qualitative reserve			35
Loss emergence period change			0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	596	544	498
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	651	723	657
Charge-offs	(444)	(450)	(595)
Recoveries	147	112	115
Net recoveries (charge-offs)	(297)	(338)	(480)
Sales/Other			(6)
Provision charged to income	266	266	396
Transfer of unallocated reserve to qualitative reserve			60
Loss emergence period change			96
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	620	651	723
Allowance for loan and lease losses \| Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance		0	89
Charge-offs			0
Recoveries			0
Net recoveries (charge-offs)			0
Sales/Other			(1)
Provision charged to income			103
Transfer of unallocated reserve to qualitative reserve			(95)
Loss emergence period change			(96)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			0
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	61	39	40
Credit for unfunded lending commitments	(3)	22	(1)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	58	61	39
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	61	39	40
Credit for unfunded lending commitments	(3)	22	(1)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	58	61	39
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
Credit for unfunded lending commitments	0	0	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	0	0	0
Reserve for unfunded lending commitments \| Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance		0	0
Credit for unfunded lending commitments			0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			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	1,256	1,260
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,274	1,256	1,260
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	605	537
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	654	605	537
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	651	723
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 620	651	723
Allowance for loan and lease losses and reserve for off-balance sheet activities, total \| Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance		$ 0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			$ 0

Amount transferred of unallocated reserve to qualitative reserve during the reporting period.

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Allowance related to loans transferred to held for sale.

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Amount transferred of unallocated reserve to qualitative reserve during the reporting period.

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

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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
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524

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-Name Accounting Standards Codification
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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))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 6
-Section L
-Subsection 1

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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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