LOANS AND LEASES - Age Analysis of Past Due Loans (Details) - USD ($) $ in Millions		Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	[1]	$ 32,151	$ 30,255
90 Days Past Due and Still Accruing		9	12
Non-accrual loans		113	113
Non-accrual with No ACL		29	26
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		80	91
Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		202	216
Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		31,949	30,039
Total commercial loans and leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		20,146	19,290
90 Days Past Due and Still Accruing		0	1
Non-accrual loans		89	84
Non-accrual with No ACL		29	26
Total commercial loans and leases | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,962	11,526
90 Days Past Due and Still Accruing		0	0
Non-accrual loans		44	39
Non-accrual with No ACL		20	15
Total commercial loans and leases | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7,462	7,131
90 Days Past Due and Still Accruing		0	1
Non-accrual loans		44	44
Non-accrual with No ACL		9	11
Total commercial loans and leases | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		562	519
90 Days Past Due and Still Accruing		0	0
Non-accrual loans		1	1
Non-accrual with No ACL		0	0
Total commercial loans and leases | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		160	114
90 Days Past Due and Still Accruing		0	0
Non-accrual loans		0	0
Non-accrual with No ACL		0	0
Total commercial loans and leases | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		23	26
Total commercial loans and leases | 30-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		15	13
Total commercial loans and leases | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7	9
Total commercial loans and leases | 30-89 Days Past Due | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		0	3
Total commercial loans and leases | 30-89 Days Past Due | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1	1
Total commercial loans and leases | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		112	111
Total commercial loans and leases | Past due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		59	52
Total commercial loans and leases | Past due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		51	54
Total commercial loans and leases | Past due | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1	4
Total commercial loans and leases | Past due | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1	1
Total commercial loans and leases | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		20,034	19,179
Total commercial loans and leases | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,903	11,474
Total commercial loans and leases | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7,411	7,077
Total commercial loans and leases | Current | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		561	515
Total commercial loans and leases | Current | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		159	113
Total consumer loans
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		12,005	10,965
90 Days Past Due and Still Accruing		9	11
Non-accrual loans		24	29
Non-accrual with No ACL		0	0
Total consumer loans | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		2,754	2,784
90 Days Past Due and Still Accruing		1	1
Non-accrual loans		6	7
Non-accrual with No ACL		0	0
Total consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		6,434	5,297
90 Days Past Due and Still Accruing		4	6
Non-accrual loans		10	14
Non-accrual with No ACL		0	0
Total consumer loans | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1,519	1,553
90 Days Past Due and Still Accruing		2	1
Non-accrual loans		2	1
Non-accrual with No ACL		0	0
Total consumer loans | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1,298	1,331
90 Days Past Due and Still Accruing		2	3
Non-accrual loans		6	7
Non-accrual with No ACL		0	0
Total consumer loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		57	65
Total consumer loans | 30-89 Days Past Due | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		5	7
Total consumer loans | 30-89 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		29	28
Total consumer loans | 30-89 Days Past Due | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		16	20
Total consumer loans | 30-89 Days Past Due | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7	10
Total consumer loans | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		90	105
Total consumer loans | Past due | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		12	15
Total consumer loans | Past due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		43	48
Total consumer loans | Past due | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		20	22
Total consumer loans | Past due | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		15	20
Total consumer loans | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,915	10,860
Total consumer loans | Current | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		2,742	2,769
Total consumer loans | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		6,391	5,249
Total consumer loans | Current | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1,499	1,531
Total consumer loans | Current | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		$ 1,283	$ 1,311

[1] Amount represents loans for which we have elected the fair value option. See Note 19.