Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	$ 124	$ 124
Other noninterest income (non-ASC 606 customer-related)	27	27
Total customer-related noninterest income	151	151
Other noncustomer-related noninterest income	5	9
Total noninterest income	156	160
Net interest income	586	679
Total net revenue	742	839
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	44	43
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	35	36
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	16	16
Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	14	13
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	14	15
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	7	8
Other noninterest income (non-ASC 606 customer-related)	9	5
Total customer-related noninterest income	16	13
Other noncustomer-related noninterest income	(1)	2
Total noninterest income	15	15
Net interest income	8	38
Total net revenue	23	53
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	(1)	(1)
Other | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	(1)	(1)
Other | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	0
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	7	9
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	38	40
Other noninterest income (non-ASC 606 customer-related)	4	7
Total customer-related noninterest income	42	47
Other noncustomer-related noninterest income	1	3
Total noninterest income	43	50
Net interest income	166	185
Total net revenue	209	235
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	13	14
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	12	13
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
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
Zions Bank | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	6	6
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
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	18	17
Other noninterest income (non-ASC 606 customer-related)	6	5
Total customer-related noninterest income	24	22
Other noncustomer-related noninterest income	2	2
Total noninterest income	26	24
Net interest income	140	160
Total net revenue	166	184
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	7	7
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	5	5
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
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
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
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	1
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	32	31
Other noninterest income (non-ASC 606 customer-related)	7	8
Total customer-related noninterest income	39	39
Other noncustomer-related noninterest income	3	2
Total noninterest income	42	41
Net interest income	113	124
Total net revenue	155	165
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	15	14
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	8	8
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	3
Amegy | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0
Amegy | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	4
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
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	10	9
Other noninterest income (non-ASC 606 customer-related)	0	1
Total customer-related noninterest income	10	10
Other noncustomer-related noninterest income	0	0
Total noninterest income	10	10
Net interest income	60	64
Total net revenue	70	74
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	2
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	4
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
NBAZ | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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
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
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	11	11
Other noninterest income (non-ASC 606 customer-related)	1	0
Total customer-related noninterest income	12	11
Other noncustomer-related noninterest income	0	0
Total noninterest income	12	11
Net interest income	47	51
Total net revenue	59	62
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	3	3
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	4	4
NSB | 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
NSB | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	0	0
NSB | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	1	1
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
Vectra | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	6	6
Other noninterest income (non-ASC 606 customer-related)	0	1
Total customer-related noninterest income	6	7
Other noncustomer-related noninterest income	0	0
Total noninterest income	6	7
Net interest income	37	41
Total net revenue	43	48
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2
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
Vectra | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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	0
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
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	2	2
Other noninterest income (non-ASC 606 customer-related)	0	0
Total customer-related noninterest income	2	2
Other noncustomer-related noninterest income	0	0
Total noninterest income	2	2
Net interest income	15	16
Total net revenue	17	18
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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
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
TCBW | Operating Segments | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)	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
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