LOANS AND LEASES - Age Analysis of Past Due Loans (Details) - USD ($) $ in Millions		Jun. 30, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	[1]	$ 31,354	$ 30,255
90 Days Past Due and Still Accruing		8	12
Non-accrual loans		143	113
Non-accrual with No ACL		30	26
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		83	91
Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		234	216
Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		31,120	30,039
Total commercial loans and leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		19,676	19,290
90 Days Past Due and Still Accruing		0	1
Non-accrual loans		117	84
Non-accrual with No ACL		30	26
Total commercial loans and leases | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,689	11,526
90 Days Past Due and Still Accruing		0	0
Non-accrual loans		42	39
Non-accrual with No ACL		19	15
Total commercial loans and leases | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7,248	7,131
90 Days Past Due and Still Accruing		0	1
Non-accrual loans		74	44
Non-accrual with No ACL		11	11
Total commercial loans and leases | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		618	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		121	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		28	26
Total commercial loans and leases | 30-89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		10	13
Total commercial loans and leases | 30-89 Days Past Due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		16	9
Total commercial loans and leases | 30-89 Days Past Due | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1	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		145	111
Total commercial loans and leases | Past due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		52	52
Total commercial loans and leases | Past due | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		90	54
Total commercial loans and leases | Past due | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		2	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		19,531	19,179
Total commercial loans and leases | Current | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,637	11,474
Total commercial loans and leases | Current | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		7,158	7,077
Total commercial loans and leases | Current | Commercial leases
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		616	515
Total commercial loans and leases | Current | Other
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		120	113
Total consumer loans
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,678	10,965
90 Days Past Due and Still Accruing		8	11
Non-accrual loans		26	29
Non-accrual with No ACL		0	0
Total consumer loans | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		2,747	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		6,089	5,297
90 Days Past Due and Still Accruing		4	6
Non-accrual loans		12	14
Non-accrual with No ACL		0	0
Total consumer loans | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1,539	1,553
90 Days Past Due and Still Accruing		1	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		1,303	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		55	65
Total consumer loans | 30-89 Days Past Due | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		6	7
Total consumer loans | 30-89 Days Past Due | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		27	28
Total consumer loans | 30-89 Days Past Due | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		14	20
Total consumer loans | 30-89 Days Past Due | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		8	10
Total consumer loans | Past due
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		89	105
Total consumer loans | Past due | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		13	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		17	22
Total consumer loans | Past due | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		16	20
Total consumer loans | Current
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		11,589	10,860
Total consumer loans | Current | Direct installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		2,734	2,769
Total consumer loans | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		6,046	5,249
Total consumer loans | Current | Indirect installment
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		1,522	1,531
Total consumer loans | Current | Consumer lines of credit
Financing Receivable, Past Due [Line Items]
Total Loans and Leases		$ 1,287	$ 1,311

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