Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 495	$ 449	$ 402
Other noninterest income (non-ASC 606 customer-related)									119	126	147
Total customer-related noninterest income									614	575	549
Other noncustomer-related noninterest income									18	128	25
Total noninterest income	$ 153	$ 165	$ 172	$ 142	$ 190	$ 139	$ 205	$ 169	632	703	574
Other real estate owned gain from sale									0	0	1
Net interest income	$ 720	$ 663	$ 593	$ 544	$ 553	$ 555	$ 555	$ 545	2,520	2,208	2,216
Total net revenue									$ 3,152	2,911	2,791
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									79.00%
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 159	137	132
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									149	135	113
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									73	73	68
Capital markets and foreign exchange fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	6	5
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									51	46	38
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									59	52	46
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									38	37	31
Other noninterest income (non-ASC 606 customer-related)									4	(6)	15
Total customer-related noninterest income									42	31	46
Other noncustomer-related noninterest income									6	109	21
Total noninterest income									48	140	67
Other real estate owned gain from sale									0	0	0
Net interest income									31	38	20
Total net revenue									79	178	87
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	1	2
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	1	0
Other | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	1	0
Other | Capital markets and foreign exchange fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	6	7
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	(2)	1
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									31	30	21
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									160	154	136
Other noninterest income (non-ASC 606 customer-related)									19	21	23
Total customer-related noninterest income									179	175	159
Other noncustomer-related noninterest income									5	10	(1)
Total noninterest income									184	185	158
Other real estate owned gain from sale									0	0	0
Net interest income									741	633	650
Total net revenue									925	818	808
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									53	46	43
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									55	58	50
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)									22	22	21
Zions Bank | Operating Segments | Capital markets and foreign exchange fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									0	0	(2)
Zions Bank | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									22	21	17
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	7	7
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									70	63	56
Other noninterest income (non-ASC 606 customer-related)									34	34	36
Total customer-related noninterest income									104	97	92
Other noncustomer-related noninterest income									4	5	3
Total noninterest income									108	102	95
Other real estate owned gain from sale									0	0	1
Net interest income									595	536	512
Total net revenue									703	638	608
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									28	25	23
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									20	17	13
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)									12	12	11
CB&T | Operating Segments | Capital markets and foreign exchange 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	5	4
CB&T | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									6	4	5
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									117	103	98
Other noninterest income (non-ASC 606 customer-related)									40	36	34
Total customer-related noninterest income									157	139	132
Other noncustomer-related noninterest income									1	2	1
Total noninterest income									158	141	133
Other real estate owned gain from sale									0	0	0
Net interest income									513	462	485
Total net revenue									671	603	618
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									46	40	42
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									33	29	24
Amegy | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									16	15	15
Amegy | Operating Segments | Capital markets and foreign exchange 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)									15	13	10
Amegy | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	6	7
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									38	31	28
Other noninterest income (non-ASC 606 customer-related)									8	13	12
Total customer-related noninterest income									46	44	40
Other noncustomer-related noninterest income									2	2	1
Total noninterest income									48	46	41
Other real estate owned gain from sale									0	0	0
Net interest income									241	204	216
Total net revenue									289	250	257
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	7	7
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									15	11	10
NBAZ | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	9	8
NBAZ | Operating Segments | Capital markets and foreign exchange 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	2
NBAZ | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	1	1
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									42	36	31
Other noninterest income (non-ASC 606 customer-related)									6	14	12
Total customer-related noninterest income									48	50	43
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									48	50	43
Other real estate owned gain from sale									0	0	0
Net interest income									183	146	146
Total net revenue									231	196	189
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									11	9	8
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									15	12	10
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	9
NSB | Operating Segments | Capital markets and foreign exchange 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	4	3
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	21	19
Other noninterest income (non-ASC 606 customer-related)									6	12	13
Total customer-related noninterest income									31	33	32
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									31	33	32
Other real estate owned gain from sale									0	0	0
Net interest income									153	136	135
Total net revenue									184	169	167
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									8	7	6
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	6	5
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 and foreign exchange 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	2	1
Vectra | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									3	2	3
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									5	4	3
Other noninterest income (non-ASC 606 customer-related)									2	2	2
Total customer-related noninterest income									7	6	5
Other noncustomer-related noninterest income									0	0	0
Total noninterest income									7	6	5
Other real estate owned gain from sale									0	0	0
Net interest income									63	53	52
Total net revenue									70	59	57
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	2	1
TCBW | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	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
TCBW | Operating Segments | Capital markets and foreign exchange 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)									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)									$ 1	$ 1	$ 1