ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Troubled Debt Restructuring [Line Items]
Retained earnings		$ (7,978)	$ (6,445)
Income tax expense		(658)	(241)	$ (460)
Allowance for credit losses		1,758	2,443
Charge-offs		325
Provision for credit losses		(411)	1,616	393
Loans and leases		128,163	123,090
Mortgage loans collateralized by residential real estate property		142	119
Charge-offs from modification of loans		6	51	7
TDR's that defaulted within 12 months of modification date		118	100	38
Allowance, Credit Loss
Financing Receivable, Troubled Debt Restructuring [Line Items]
Allowance for credit losses		1,934	2,670	1,296
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Financing Receivable, Troubled Debt Restructuring [Line Items]
Retained earnings	$ 337
Income tax expense	114
Allowance for credit losses	$ 451
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Charge-offs increase (decrease)		(261)
Allowance for credit losses, individually evaluated for impairment		5
Loans and leases		60,350	60,793
TDR's that defaulted within 12 months of modification date		23	54	1
Commercial | Allowance, Credit Loss
Financing Receivable, Troubled Debt Restructuring [Line Items]
Allowance for credit losses		974	1,419	718
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Charge-offs increase (decrease)		(107)
Loans and leases		67,813	62,297
TDR's that defaulted within 12 months of modification date		95	46	37
Retail | Allowance, Credit Loss
Financing Receivable, Troubled Debt Restructuring [Line Items]
Allowance for credit losses		960	1,251	$ 578
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		44,500	44,173
Collateral Dependent | Home Equity Loan And Residential Mortgages | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		542	552
Collateral Dependent | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		$ 103	$ 206