Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 503	$ 495	$ 449
Other noninterest income (non-ASC 606 customer-related)									117	119	126
Total customer-related noninterest income									620	614	575
Other noncustomer-related noninterest income									57	18	128
Total noninterest income	$ 148	$ 180	$ 189	$ 160	$ 153	$ 165	$ 172	$ 142	677	632	703
Net interest income	$ 583	$ 585	$ 591	$ 679	$ 720	$ 663	$ 593	$ 544	2,438	2,520	2,208
Total net revenue									$ 3,115	3,152	2,911
Interest income on loans and securities | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Segment Reporting, Revenue Reconciling Item [Line Items]
Percentage of revenue									81.00%
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 174	159	137
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									146	149	135
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									66	73	73
Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	4	6
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									53	51	46
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									60	59	52
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									34	38	37
Other noninterest income (non-ASC 606 customer-related)									14	4	(6)
Total customer-related noninterest income									48	42	31
Other noncustomer-related noninterest income									17	6	109
Total noninterest income									65	48	140
Net interest income									30	31	38
Total net revenue									95	79	178
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	2	1
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	0	1
Other | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	0	1
Other | Capital markets fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	4	6
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									(1)	1	(2)
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									31	31	30
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									157	160	154
Other noninterest income (non-ASC 606 customer-related)									24	19	21
Total customer-related noninterest income									181	179	175
Other noncustomer-related noninterest income									11	5	10
Total noninterest income									192	184	185
Net interest income									696	741	633
Total net revenue									888	925	818
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									55	53	46
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									52	55	58
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)									19	22	22
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
Zions Bank | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									23	22	21
Zions Bank | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									8	8	7
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									75	70	63
Other noninterest income (non-ASC 606 customer-related)									35	34	34
Total customer-related noninterest income									110	104	97
Other noncustomer-related noninterest income									6	4	5
Total noninterest income									116	108	102
Net interest income									598	595	536
Total net revenue									714	703	638
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									32	28	25
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									21	20	17
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)									11	12	12
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
CB&T | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	4	5
CB&T | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	6	4
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									125	117	103
Other noninterest income (non-ASC 606 customer-related)									37	40	36
Total customer-related noninterest income									162	157	139
Other noncustomer-related noninterest income									22	1	2
Total noninterest income									184	158	141
Net interest income									453	513	462
Total net revenue									637	671	603
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									56	46	40
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									31	33	29
Amegy | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									14	16	15
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
Amegy | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									17	15	13
Amegy | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	7	6
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									37	38	31
Other noninterest income (non-ASC 606 customer-related)									2	8	13
Total customer-related noninterest income									39	46	44
Other noncustomer-related noninterest income									1	2	2
Total noninterest income									40	48	46
Net interest income									260	241	204
Total net revenue									300	289	250
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									10	9	7
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									15	15	11
NBAZ | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									8	9	9
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
NBAZ | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									3	3	3
NBAZ | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	2	1
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									44	42	36
Other noninterest income (non-ASC 606 customer-related)									1	6	14
Total customer-related noninterest income									45	48	50
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									45	48	50
Net interest income									191	183	146
Total net revenue									236	231	196
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									12	11	9
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									16	15	12
NSB | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									10	10	10
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
NSB | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									5	5	4
NSB | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	1	1
Vectra | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									25	25	21
Other noninterest income (non-ASC 606 customer-related)									3	6	12
Total customer-related noninterest income									28	31	33
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									28	31	33
Net interest income									150	153	136
Total net revenue									178	184	169
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	8	7
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	9	6
Vectra | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	4	4
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
Vectra | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	1	2
Vectra | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	3	2
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									6	5	4
Other noninterest income (non-ASC 606 customer-related)									1	2	2
Total customer-related noninterest income									7	7	6
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									7	7	6
Net interest income									60	63	53
Total net revenue									67	70	59
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	2	2
TCBW | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	2	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
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
TCBW | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	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)									$ 1	$ 1	$ 1