Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 449	$ 402	$ 414
Other noninterest income (Non-ASC 606 customer related)									126	147	111
Total customer-related fees									575	549	525
Other noninterest income (noncustomer-related)									128	25	37
Total noninterest income	$ 190	$ 139	$ 205	$ 169	$ 166	$ 157	$ 117	$ 134	703	574	562
Other real estate owned gain from sale									0	1	4
Net interest income	$ 553	$ 555	$ 555	$ 545	$ 550	$ 555	$ 563	$ 548	2,208	2,216	2,272
Total income less interest expense									$ 2,911	2,791	2,838
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									76.00%
Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									$ 134	125	121
Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									135	113	127
Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									73	68	78
Capital markets and foreign exchange fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	12	13
Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									46	38	34
Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									52	46	41
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									37	31	37
Other noninterest income (Non-ASC 606 customer related)									(6)	15	3
Total customer-related fees									31	46	40
Other noninterest income (noncustomer-related)									109	21	33
Total noninterest income									140	67	73
Other real estate owned gain from sale									0	0	0
Net interest income									32	20	24
Total income less interest expense									172	87	97
Other | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	2	0
Other | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	0	2
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 and foreign exchange fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	8	7
Other | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									(2)	1	(2)
Other | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									30	20	29
Zions Bank | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									154	136	134
Other noninterest income (Non-ASC 606 customer related)									21	23	12
Total customer-related fees									175	159	146
Other noninterest income (noncustomer-related)									10	(1)	1
Total noninterest income									185	158	147
Other real estate owned gain from sale									0	0	3
Net interest income									634	650	688
Total income less interest expense									819	808	838
Zions Bank | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									45	42	41
Zions Bank | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									58	49	51
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)									23	21	23
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	(1)	0
Zions Bank | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									21	17	16
Zions Bank | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	8	3
Amegy | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									103	98	98
Other noninterest income (Non-ASC 606 customer related)									36	34	40
Total customer-related fees									139	132	138
Other noninterest income (noncustomer-related)									2	1	0
Total noninterest income									141	133	138
Other real estate owned gain from sale									0	0	0
Net interest income									463	485	489
Total income less interest expense									604	618	627
Amegy | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									38	37	34
Amegy | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									29	24	28
Amegy | Operating Segments | Retail and business banking fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									15	15	17
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)									2	5	6
Amegy | Operating Segments | Wealth management fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									13	10	8
Amegy | Operating Segments | Other customer-related fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									6	7	5
CB&T | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									63	56	58
Other noninterest income (Non-ASC 606 customer related)									34	36	28
Total customer-related fees									97	92	86
Other noninterest income (noncustomer-related)									5	3	2
Total noninterest income									102	95	88
Other real estate owned gain from sale									0	1	0
Net interest income									537	512	512
Total income less interest expense									639	608	600
CB&T | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									25	22	23
CB&T | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									17	14	16
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	11	13
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)									5	4	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)									4	5	2
NBAZ | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									31	28	29
Other noninterest income (Non-ASC 606 customer related)									13	12	12
Total customer-related fees									44	40	41
Other noninterest income (noncustomer-related)									2	1	1
Total noninterest income									46	41	42
Other real estate owned gain from sale									0	0	0
Net interest income									205	216	223
Total income less interest expense									251	257	265
NBAZ | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	7	7
NBAZ | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									11	10	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)									9	8	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	2	2
NBAZ | 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
NSB | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									36	31	35
Other noninterest income (Non-ASC 606 customer related)									14	12	8
Total customer-related fees									50	43	43
Other noninterest income (noncustomer-related)									0	0	0
Total noninterest income									50	43	43
Other real estate owned gain from sale									0	0	1
Net interest income									147	146	148
Total income less interest expense									197	189	192
NSB | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									9	8	8
NSB | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									12	10	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	9	11
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)									4	3	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)									21	19	19
Other noninterest income (Non-ASC 606 customer related)									12	13	7
Total customer-related fees									33	32	26
Other noninterest income (noncustomer-related)									0	0	0
Total noninterest income									33	32	26
Other real estate owned gain from sale									0	0	0
Net interest income									136	135	135
Total income less interest expense									169	167	161
Vectra | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									7	6	6
Vectra | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									6	5	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	5
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)									2	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)									2	3	0
TCBW | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									4	3	4
Other noninterest income (Non-ASC 606 customer related)									2	2	1
Total customer-related fees									6	5	5
Other noninterest income (noncustomer-related)									0	0	0
Total noninterest income									6	5	5
Other real estate owned gain from sale									0	0	0
Net interest income									54	52	53
Total income less interest expense									60	57	58
TCBW | Operating Segments | Commercial account fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									2	1	2
TCBW | Operating Segments | Card fees
Segment Reporting, Revenue Reconciling Item [Line Items]
Total noninterest income from contracts with customers (ASC 606)									1	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	1
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	$ 0