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
Mar. 31, 2019	Mar. 31, 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	85	$ 78
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,245
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	1,242	1,236
Charge-offs	(138)	(116)
Recoveries	49	46
Net charge-offs	(89)	(70)
Provision charged to income	92	80
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,245	1,246
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	91	88
Provision for unfunded lending commitments	(7)	(2)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	84	86
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	1,329	1,332
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	690	685
Charge-offs	(26)	(3)
Recoveries	2	6
Net charge-offs	(24)	3
Provision charged to income	25	23
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	691	711
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	91	88
Provision for unfunded lending commitments	(7)	(2)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	84	86
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	775	797
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	552	551
Charge-offs	(112)	(113)
Recoveries	47	40
Net charge-offs	(65)	(73)
Provision charged to income	67	57
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	554	535
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
Provision for unfunded lending commitments	0	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	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	$ 554	$ 535

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

No definition available.

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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.

+ 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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