REVENUE FROM CONTRACTS WITH CUSTOMERS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	$ 128	$ 126	$ 378	$ 378
Customer-related noninterest income from other sources	33	31	88	92
Total customer-related noninterest income	161	157	466	470
Noncustomer-related noninterest income	11	23	41	59
Noninterest income	172	180	507	529
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	46	43	135	131
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	36	37	108	110
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	17	17	50	49
Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	1	4	2
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	13	14	40	41
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	14	14	41	45
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	8	6	24	24
Customer-related noninterest income from other sources	4	3	16	12
Total customer-related noninterest income	12	9	40	36
Noncustomer-related noninterest income	7	16	19	24
Noninterest income	19	25	59	60
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	(1)	(1)	1	0
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	(1)	1	1
Other | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	(1)	0	1	1
Other | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	1	4	2
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	(1)	0	0	(2)
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	8	7	17	22
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	39	41	117	120
Customer-related noninterest income from other sources	7	6	16	19
Total customer-related noninterest income	46	47	133	139
Noncustomer-related noninterest income	0	2	3	9
Noninterest income	46	49	136	148
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	15	14	42	42
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	12	13	38	39
Zions Bank | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	5	5	14	14
Zions Bank | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
Zions Bank | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	5	7	16	19
Zions Bank | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	2	7	6
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	19	19	55	56
Customer-related noninterest income from other sources	10	7	26	26
Total customer-related noninterest income	29	26	81	82
Noncustomer-related noninterest income	2	2	6	5
Noninterest income	31	28	87	87
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	8	8	23	24
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	5	5	14	15
CB&T | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	3	3	9	8
CB&T | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
CB&T | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	1	3	3
CB&T | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	2	6	6
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	32	31	95	94
Customer-related noninterest income from other sources	10	12	25	29
Total customer-related noninterest income	42	43	120	123
Noncustomer-related noninterest income	2	3	8	20
Noninterest income	44	46	128	143
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	15	14	44	42
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	8	8	23	24
Amegy | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	4	3	10	10
Amegy | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
Amegy | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	4	4	13	13
Amegy | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	2	5	5
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	10	9	29	28
Customer-related noninterest income from other sources	1	1	2	2
Total customer-related noninterest income	11	10	31	30
Noncustomer-related noninterest income	0	0	0	1
Noninterest income	11	10	31	31
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	3	2	8	7
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	4	4	11	11
NBAZ | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	2	6	6
NBAZ | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
NBAZ | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	1	3	3
NBAZ | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	1	1
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	12	11	34	33
Customer-related noninterest income from other sources	0	1	1	1
Total customer-related noninterest income	12	12	35	34
Noncustomer-related noninterest income	0	0	5	0
Noninterest income	12	12	40	34
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	3	3	10	9
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	4	4	12	12
NSB | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	3	3	7	7
NSB | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
NSB | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	1	4	4
NSB | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	1	1
Vectra | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	7	7	20	19
Customer-related noninterest income from other sources	0	1	0	2
Total customer-related noninterest income	7	8	20	21
Noncustomer-related noninterest income	0	0	0	0
Noninterest income	7	8	20	21
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	2	5	5
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	2	3	8	7
Vectra | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	1	3	3
Vectra | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
Vectra | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	0	1	1
Vectra | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	1	3	3
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	2	4	4
Customer-related noninterest income from other sources	1	0	2	1
Total customer-related noninterest income	2	2	6	5
Noncustomer-related noninterest income	0	0	0	0
Noninterest income	2	2	6	5
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	1	1	2	2
TCBW | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	1	1	1
TCBW | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
TCBW | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
TCBW | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	0	0	0	0
TCBW | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers	$ 0	$ 0	$ 1	$ 1