Operating Segment Information (Details) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Jul. 31, 2022 branch	Dec. 31, 2023 USD ($) branch	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) branch segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of bank operating segments | segment										7
Number of branches | branch		407								407
Total deposits		$ 74,961				$ 71,652				$ 74,961	$ 71,652
Loans held for investment, net of allowance		57,095				55,078				57,095	55,078
Net interest income		583	$ 585	$ 591	$ 679	720	$ 663	$ 593	$ 544	2,438	2,520	$ 2,208
Provision for credit losses		0	41	46	45	43	71	41	(33)	132	122	(276)
Net interest income after provision for credit losses										2,306	2,398	2,484
Noninterest income		148	180	189	160	153	165	172	142	677	632	703
Noninterest expense		581	496	508	512	471	479	464	464	2,097	1,878	1,741
Income (loss) before income taxes		$ 150	$ 228	$ 226	$ 282	$ 359	$ 278	$ 260	$ 255	886	1,152	1,446
Total average loans										56,740	52,598	51,983
Total average deposits										72,866	78,529	76,257
Other
Segment Reporting Information [Line Items]
Net interest income										30	31	38
Provision for credit losses										(2)	0	1
Net interest income after provision for credit losses										32	31	37
Noninterest income										65	48	140
Noninterest expense										224	226	201
Income (loss) before income taxes										(127)	(147)	(24)
Total average loans										1,044	922	857
Total average deposits										6,161	1,166	1,475
Zions Bank | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										696	741	633
Provision for credit losses										20	43	(26)
Net interest income after provision for credit losses										676	698	659
Noninterest income										192	184	185
Noninterest expense										557	495	464
Income (loss) before income taxes										311	387	380
Total average loans										14,298	13,277	13,198
Total average deposits										20,233	24,317	23,588
CB&T | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										598	595	536
Provision for credit losses										44	49	(78)
Net interest income after provision for credit losses										554	546	614
Noninterest income										116	108	102
Noninterest expense										388	340	311
Income (loss) before income taxes										282	314	405
Total average loans										14,128	13,129	12,892
Total average deposits										14,253	16,160	15,796
Amegy | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										453	513	462
Provision for credit losses										15	5	(96)
Net interest income after provision for credit losses										438	508	558
Noninterest income										184	158	141
Noninterest expense										404	355	337
Income (loss) before income taxes										218	311	362
Total average loans										12,851	12,110	12,189
Total average deposits										13,569	15,735	15,496
NBAZ | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										260	241	204
Provision for credit losses										4	11	(27)
Net interest income after provision for credit losses										256	230	231
Noninterest income										40	48	46
Noninterest expense										189	167	151
Income (loss) before income taxes										107	111	126
Total average loans										5,318	4,911	4,849
Total average deposits										7,008	8,035	7,288
NSB | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										191	183	146
Provision for credit losses										42	4	(35)
Net interest income after provision for credit losses										149	179	181
Noninterest income										45	48	50
Noninterest expense										171	151	142
Income (loss) before income taxes										23	76	89
Total average loans										3,392	2,987	3,015
Total average deposits										6,964	7,436	6,691
Vectra | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										150	153	136
Provision for credit losses										7	9	(12)
Net interest income after provision for credit losses										143	144	148
Noninterest income										28	31	33
Noninterest expense										137	120	114
Income (loss) before income taxes										34	55	67
Total average loans										4,004	3,632	3,414
Total average deposits										3,482	4,109	4,386
TCBW | Operating Segments
Segment Reporting Information [Line Items]
Net interest income										60	63	53
Provision for credit losses										2	1	(3)
Net interest income after provision for credit losses										58	62	56
Noninterest income										7	7	6
Noninterest expense										27	24	21
Income (loss) before income taxes										38	45	41
Total average loans										1,705	1,630	1,569
Total average deposits										$ 1,196	$ 1,571	$ 1,537
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		75								75
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		43								43
Number of Branches Purchased | branch	3
Colorado | Vectra
Segment Reporting Information [Line Items]
Number of branches | branch		33								33
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