ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Summary of Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	$ 2,443
Charge-offs	(325)
Provision for credit losses	(411)	$ 1,616	$ 393
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,758	2,443
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	2,443	1,252	1,242
Charge-offs	(539)	(843)	(615)
Recoveries	214	150	185
Net charge-offs	(325)	(693)	(430)
Provision for credit losses	(360)	1,431	440
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,758	2,443	1,252
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	227	44	91
Provision for unfunded lending commitments	(51)	185	(47)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	176	227	44
Allowance, Credit Loss
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	2,670	1,296
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	1,934	2,670	1,296
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	1,233	674	690
Charge-offs	(218)	(437)	(140)
Recoveries	54	12	24
Net charge-offs	(164)	(425)	(116)
Provision for credit losses	(248)	1,160	100
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	821	1,233	674
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	186	44	91
Provision for unfunded lending commitments	(33)	145	(47)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	153	186	44
Commercial \| Allowance, Credit Loss
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	1,419	718
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	974	1,419	718
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	1,210	578	552
Charge-offs	(321)	(406)	(475)
Recoveries	160	138	161
Net charge-offs	(161)	(268)	(314)
Provision for credit losses	(112)	271	340
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	937	1,210	578
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	41	0	0
Provision for unfunded lending commitments	(18)	40	0
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	23	41	0
Retail \| Allowance, Credit Loss
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Beginning balance	1,251	578
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance	$ 960	1,251	578
Cumulative Effect, Period of Adoption, Adjustment \| 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		453
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			453
Cumulative Effect, Period of Adoption, Adjustment \| 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		(2)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			(2)
Cumulative Effect, Period of Adoption, Adjustment \| 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		(176)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			(176)
Cumulative Effect, Period of Adoption, Adjustment \| 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		(3)
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			(3)
Cumulative Effect, Period of Adoption, Adjustment \| 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		629
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			629
Cumulative Effect, Period of Adoption, Adjustment \| 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		1
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			1
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		1,705
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			1,705
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		42
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			42
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		498
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			498
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		41
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			41
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		1,207
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			1,207
Cumulative Effect, Period Of Adoption, Adjusted Balance \| 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		$ 1
Allowance for loan and lease losses / Reserve for unfunded lending commitments, Ending balance			$ 1

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- Definition

Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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