Operating Segment Information (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jul. 31, 2022 branch	Dec. 31, 2022 USD ($) branch	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2022 USD ($) branch segment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of bank operating segments | segment										7
Number of branches | branch		416								416
Total deposits		$ 71,652				$ 82,789				$ 71,652	$ 82,789
Loans held for investment, net of allowance		55,078				50,338				55,078	50,338
Net interest income		720	$ 663	$ 593	$ 544	553	$ 555	$ 555	$ 545	2,520	2,208	$ 2,216
Provision for credit losses		43	71	41	(33)	25	(46)	(123)	(132)	122	(276)	414
Net interest income after provision for credit losses										2,398	2,484	1,802
Noninterest income		153	165	172	142	190	139	205	169	632	703	574
Noninterest expense		471	479	464	464	449	429	428	435	1,878	1,741	1,704
Income (loss) before income taxes		$ 359	$ 278	$ 260	$ 255	$ 269	$ 311	$ 455	$ 411	1,152	1,446	672
Total average loans										52,598	51,983	53,016
Total average deposits										78,529	76,257	63,689
Other
Segment Reporting Information [Line Items]
Net interest income										31	38	20
Provision for credit losses										0	1	3
Net interest income after provision for credit losses										31	37	17
Noninterest income										48	140	67
Noninterest expense										226	201	205
Income (loss) before income taxes										(147)	(24)	(121)
Total average loans										922	857	629
Total average deposits										1,166	1,475	2,495
Zions Bank | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										741	633	650
Provision for credit losses										43	(26)	67
Net interest income after provision for credit losses										698	659	583
Noninterest income										184	185	158
Noninterest expense										495	464	446
Income (loss) before income taxes										387	380	295
Total average loans										13,277	13,198	13,845
Total average deposits										24,317	23,588	18,370
CB&T | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										595	536	512
Provision for credit losses										49	(78)	120
Net interest income after provision for credit losses										546	614	392
Noninterest income										108	102	95
Noninterest expense										340	311	305
Income (loss) before income taxes										314	405	182
Total average loans										13,129	12,892	12,366
Total average deposits										16,160	15,796	13,763
Amegy | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										513	462	485
Provision for credit losses										5	(96)	111
Net interest income after provision for credit losses										508	558	374
Noninterest income										158	141	133
Noninterest expense										355	337	329
Income (loss) before income taxes										311	362	178
Total average loans										12,110	12,189	13,114
Total average deposits										15,735	15,496	12,970
NBAZ | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										241	204	216
Provision for credit losses										11	(27)	35
Net interest income after provision for credit losses										230	231	181
Noninterest income										48	46	41
Noninterest expense										167	151	147
Income (loss) before income taxes										111	126	75
Total average loans										4,911	4,849	5,099
Total average deposits										8,035	7,288	5,771
NSB | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										183	146	146
Provision for credit losses										4	(35)	37
Net interest income after provision for credit losses										179	181	109
Noninterest income										48	50	43
Noninterest expense										151	142	141
Income (loss) before income taxes										76	89	11
Total average loans										2,987	3,015	3,102
Total average deposits										7,436	6,691	5,427
Vectra | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										153	136	135
Provision for credit losses										9	(12)	34
Net interest income after provision for credit losses										144	148	101
Noninterest income										31	33	32
Noninterest expense										120	114	109
Income (loss) before income taxes										55	67	24
Total average loans										3,632	3,414	3,401
Total average deposits										4,109	4,386	3,637
TCBW | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										63	53	52
Provision for credit losses										1	(3)	7
Net interest income after provision for credit losses										62	56	45
Noninterest income										7	6	5
Noninterest expense										24	21	22
Income (loss) before income taxes										45	41	28
Total average loans										1,630	1,569	1,460
Total average deposits										$ 1,571	$ 1,537	$ 1,256
Utah | Zions Bank
Segment Reporting Information [Line Items]
Number of branches | branch		95								95
Idaho | Zions Bank
Segment Reporting Information [Line Items]
Number of branches | branch		25								25
Wyoming | Zions Bank
Segment Reporting Information [Line Items]
Number of branches | branch		1								1
California | CB&T
Segment Reporting Information [Line Items]
Number of branches | branch		80								80
Texas | Amegy
Segment Reporting Information [Line Items]
Number of branches | branch		75								75
Arizona | NBAZ
Segment Reporting Information [Line Items]
Number of branches | branch		56								56
Nevada | NSB
Segment Reporting Information [Line Items]
Number of branches | branch		46								46
Number of Branches Purchased | branch	3
Colorado | Vectra
Segment Reporting Information [Line Items]
Number of branches | branch		34								34
New Mexico | Vectra
Segment Reporting Information [Line Items]
Number of branches | branch		1								1
Washington | TCBW
Segment Reporting Information [Line Items]
Number of branches | branch		2								2
Oregon | TCBW
Segment Reporting Information [Line Items]
Number of branches | branch		1								1