Operating Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024 USD ($) branch	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) branch segment	Jun. 30, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of bank operating segments | segment			7
Number of branches | branch	408		408
Net interest income	$ 597	$ 591	$ 1,183	$ 1,270
Provision for credit losses	5	46	18	91
Net interest income after provision for credit losses	592	545	1,165	1,179
Noninterest income	179	189	335	349
Noninterest expense	509	508	1,035	1,020
Income before income taxes	262	226	465	508
Total average loans	58,291	56,679	58,100	56,417
Total average deposits	74,228	69,649	73,793	69,901
Other
Segment Reporting Information [Line Items]
Net interest income	4	(21)	14	18
Provision for credit losses	(2)	(1)	(3)	(1)
Net interest income after provision for credit losses	6	(20)	17	19
Noninterest income	25	19	42	35
Noninterest expense	(1)	49	36	109
Income before income taxes	32	(50)	23	(55)
Total average loans	941	1,040	962	1,092
Total average deposits	5,452	7,379	5,083	4,720
Zions Bank | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	171	178	336	363
Provision for credit losses	(7)	7	(18)	31
Net interest income after provision for credit losses	178	171	354	332
Noninterest income	47	49	90	99
Noninterest expense	151	138	291	273
Income before income taxes	74	82	153	158
Total average loans	14,893	14,250	14,808	14,115
Total average deposits	20,906	19,191	20,820	20,067
CB&T | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	144	152	284	311
Provision for credit losses	(5)	15	17	15
Net interest income after provision for credit losses	149	137	267	296
Noninterest income	30	35	56	59
Noninterest expense	103	94	204	186
Income before income taxes	76	78	119	169
Total average loans	14,127	14,152	14,146	14,084
Total average deposits	14,539	13,333	14,473	13,985
Amegy | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	119	116	232	240
Provision for credit losses	14	12	18	23
Net interest income after provision for credit losses	105	104	214	217
Noninterest income	42	55	83	96
Noninterest expense	116	100	229	198
Income before income taxes	31	59	68	115
Total average loans	13,345	12,880	13,230	12,862
Total average deposits	14,612	11,873	14,742	12,576
NBAZ | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	59	64	119	129
Provision for credit losses	(1)	4	5	4
Net interest income after provision for credit losses	60	60	114	125
Noninterest income	10	11	20	21
Noninterest expense	51	45	99	92
Income before income taxes	19	26	35	54
Total average loans	5,595	5,243	3,527	5,197
Total average deposits	6,929	6,873	7,203	7,025
NSB | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	49	49	96	99
Provision for credit losses	7	7	2	11
Net interest income after provision for credit losses	42	42	94	88
Noninterest income	16	11	28	23
Noninterest expense	45	42	89	82
Income before income taxes	13	11	33	29
Total average loans	3,547	3,427	3,527	3,377
Total average deposits	7,207	6,630	7,203	6,800
Vectra | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	36	38	73	79
Provision for credit losses	0	2	(6)	6
Net interest income after provision for credit losses	36	36	79	73
Noninterest income	7	7	13	13
Noninterest expense	36	34	70	67
Income before income taxes	7	9	22	19
Total average loans	4,088	3,998	4,063	3,990
Total average deposits	3,475	3,271	3,463	3,488
TCBW | Operating Segments
Segment Reporting Information [Line Items]
Net interest income	15	15	29	31
Provision for credit losses	(1)	0	3	2
Net interest income after provision for credit losses	16	15	26	29
Noninterest income	2	2	3	3
Noninterest expense	8	6	17	13
Income before income taxes	10	11	12	19
Total average loans	1,755	1,689	1,741	1,700
Total average deposits	$ 1,108	$ 1,099	$ 1,115	$ 1,240
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
Texas | Amegy
Segment Reporting Information [Line Items]
Number of branches | branch	75		75
California | CB&T
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
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