Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	$ 126	$ 128	$ 251	$ 251
Other noninterest income (non-ASC 606 customer-related)	28	34	54	62
Total customer-related noninterest income	154	162	305	313
Other noncustomer-related noninterest income	25	27	30	36
Total noninterest income	179	189	335	349
Other real estate owned gain from sale	1	0	1	0
Net interest income	597	591	1,183	1,270
Total net revenue	777	780	1,519	1,619
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	45	45	89	88
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	37	37	72	72
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	16	16	33	32
Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	2	2
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	13	14	27	27
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	14	15	28	30
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	6	8	16	16
Other noninterest income (non-ASC 606 customer-related)	4	5	10	11
Total customer-related noninterest income	10	13	26	27
Other noncustomer-related noninterest income	15	6	16	8
Total noninterest income	25	19	42	35
Other real estate owned gain from sale	0	0	0	0
Net interest income	4	(21)	14	18
Total net revenue	29	(2)	56	53
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	(1)	1	1	1
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
Other | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	(2)	0	(1)
Other | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	2	2
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	(1)	0	(1)	(1)
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	7	8	14	15
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	39	40	77	79
Other noninterest income (non-ASC 606 customer-related)	6	6	10	13
Total customer-related noninterest income	45	46	87	92
Other noncustomer-related noninterest income	2	3	3	7
Total noninterest income	47	49	90	99
Other real estate owned gain from sale	1	0	1	0
Net interest income	171	178	336	363
Total net revenue	219	227	427	462
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	14	14	28	28
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	13	13	25	26
Zions Bank | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	5	5	9	9
Zions Bank | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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 (ASC 606)	5	6	11	12
Zions Bank | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	4	4
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	18	19	37	37
Other noninterest income (non-ASC 606 customer-related)	10	14	16	19
Total customer-related noninterest income	28	33	53	56
Other noncustomer-related noninterest income	2	2	3	3
Total noninterest income	30	35	56	59
Other real estate owned gain from sale	0	0	0	0
Net interest income	144	152	284	311
Total net revenue	174	187	340	370
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	8	8	15	15
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	5	10	10
CB&T | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	3	6	6
CB&T | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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 (ASC 606)	1	1	2	2
CB&T | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	4	4
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	32	32	63	62
Other noninterest income (non-ASC 606 customer-related)	7	8	15	17
Total customer-related noninterest income	39	40	78	79
Other noncustomer-related noninterest income	3	15	5	17
Total noninterest income	42	55	83	96
Other real estate owned gain from sale	0	0	0	0
Net interest income	119	116	232	240
Total net revenue	161	171	315	336
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	14	14	29	28
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	8	8	15	16
Amegy | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	4	7	7
Amegy | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
Amegy | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	5	4	9	8
Amegy | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	3	3
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	10	9	20	19
Other noninterest income (non-ASC 606 customer-related)	1	1	1	1
Total customer-related noninterest income	11	10	21	20
Other noncustomer-related noninterest income	(1)	1	(1)	1
Total noninterest income	10	11	20	21
Other real estate owned gain from sale	0	0	0	0
Net interest income	59	64	119	129
Total net revenue	69	75	139	150
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	2	5	5
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	4	8	7
NBAZ | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	4	4
NBAZ | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
NBAZ | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	2	2
NBAZ | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	1	1
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	12	11	23	23
Other noninterest income (non-ASC 606 customer-related)	0	0	1	0
Total customer-related noninterest income	12	11	24	23
Other noncustomer-related noninterest income	4	0	4	0
Total noninterest income	16	11	28	23
Other real estate owned gain from sale	0	0	0	0
Net interest income	49	49	96	99
Total net revenue	65	60	124	122
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	3	7	7
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	4	8	8
NSB | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	3	5	5
NSB | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
NSB | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	1	3	3
NSB | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
Vectra | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	7	7	13	12
Other noninterest income (non-ASC 606 customer-related)	0	0	0	1
Total customer-related noninterest income	7	7	13	13
Other noncustomer-related noninterest income	0	0	0	0
Total noninterest income	7	7	13	13
Other real estate owned gain from sale	0	0	0	0
Net interest income	36	38	73	79
Total net revenue	43	45	86	92
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	3	3
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	2	5	4
Vectra | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	2	2
Vectra | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
Vectra | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	1	1	1
Vectra | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	2	2
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2	2	3
Other noninterest income (non-ASC 606 customer-related)	0	0	1	0
Total customer-related noninterest income	2	2	3	3
Other noncustomer-related noninterest income	0	0	0	0
Total noninterest income	2	2	3	3
Other real estate owned gain from sale	0	0	0	0
Net interest income	15	15	29	31
Total net revenue	17	17	32	34
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1	1	1
TCBW | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	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 (ASC 606)	0	0	0	0
TCBW | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0	0	0
TCBW | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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 (ASC 606)	$ 0	$ 0	$ 0	$ 1