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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance			$ 1,242
Provision charged to income			182	$ 163
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 1,227		1,227
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	1,245	$ 1,246	1,242	1,236
Charge-offs	(156)	(120)	(294)	(236)
Recoveries	50	44	99	90
Net charge-offs	(106)	(76)	(195)	(146)
Provision charged to income	88	83	180	163
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,227	1,253	1,227	1,253
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	84	86	91	88
Provision for unfunded lending commitments	9	2	2	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	93	88	93	88
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	1,320	1,341	1,320	1,341
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	691	711	690	685
Charge-offs	(45)	(14)	(71)	(17)
Recoveries	12	2	14	8
Net charge-offs	(33)	(12)	(57)	(9)
Provision charged to income	22	16	47	39
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	680	715	680	715
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	84	86	91	88
Provision for unfunded lending commitments	9	2	2	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	93	88	93	88
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	773	803	773	803
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	554	535	552	551
Charge-offs	(111)	(106)	(223)	(219)
Recoveries	38	42	85	82
Net charge-offs	(73)	(64)	(138)	(137)
Provision charged to income	66	67	133	124
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	547	538	547	538
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	$ 547	$ 538	$ 547	$ 538

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.

+ References

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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.

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

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