Operating Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) Branches Banks	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) Branches Banks	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Net interest income	$ 480,470	$ 469,187	$ 464,849	$ 452,842	$ 448,833	$ 425,377	$ 423,704	$ 417,346	$ 1,867,348	$ 1,715,260	$ 1,680,004
Provision for loan losses	(2,687)	18,825	34,492	42,145	22,701	18,262	566	(1,494)	92,775	40,035	(98,082)
Loans and Leases Receivable, Net of Deferred Income	42,649,265				40,649,542				42,649,265	40,649,542
Deposits	(53,235,830)				(50,374,091)				(53,235,830)	(50,374,091)
Carrying value, Preferred stock	709,601				828,490				709,601	828,490
Net interest income after provision for loan losses									1,774,573	1,675,225	1,778,086
Net impairment losses on investment securities									0	0	(27)
Noninterest Income									515,609	357,241	492,704
Noninterest expense	404,515	403,292	381,894	395,573	397,353	391,280	398,997	392,977	1,585,274	1,580,607	1,649,367
Income (loss) before income taxes	206,886	191,957	174,180	131,885	147,420	141,779	19,459	143,201	704,908	451,859	621,423
Income Tax Expense (Benefit)									235,858	142,388	222,961
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	137,401	$ 127,263	$ 113,949	$ 90,437	102,487	$ 100,999	$ 13,960	$ 92,025	469,050	309,471	398,462
Cash and due from banks	$ 737,327				798,319				$ 737,327	798,319	841,942	$ 1,173,057
Number of community/regional banks operating in distinct geographical areas | Banks	7								7
Total shareholders' equity	$ 7,634,306				7,507,519				$ 7,634,306	7,507,519	7,369,530	$ 6,464,563
Zions Bank [Member]
Segment Reporting Information [Line Items]
Net interest income									633,100	614,900	628,800
Provision for loan losses									(21,600)	(28,300)	(58,500)
Deposits	(16,764,000)				(16,233,000)				(16,764,000)	(16,233,000)	(16,214,000)
Net interest income after provision for loan losses									654,700	643,200	687,300
Noninterest Income									148,600	132,700	143,000
Noninterest expense									392,500	430,700	439,900
Income (loss) before income taxes									410,800	345,200	390,400
Average Loans	$ 12,560,000				12,232,000				$ 12,560,000	12,232,000	12,172,000
California Bank Trust [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	93								93
Amegy [Member]
Segment Reporting Information [Line Items]
Net interest income									$ 479,500	475,400	466,400
Provision for loan losses									163,000	91,300	32,200
Deposits	$ (11,924,000)				(11,677,000)				(11,924,000)	(11,677,000)	(11,491,000)
Net interest income after provision for loan losses									316,500	384,100	434,200
Noninterest Income									122,500	120,600	127,500
Noninterest expense									317,100	372,700	357,300
Income (loss) before income taxes									121,900	132,000	204,400
Average Loans	$ 10,557,000				10,115,000				$ 10,557,000	10,115,000	10,077,000
Number of Branches | Branches	74								74
California Bank And Trust [Member]
Segment Reporting Information [Line Items]
Net interest income									$ 450,000	425,600	444,100
Provision for loan losses									(9,100)	(4,400)	(20,100)
Deposits	$ (10,969,000)				(10,520,000)				(10,969,000)	(10,520,000)	(9,707,000)
Net interest income after provision for loan losses									459,100	430,000	464,200
Noninterest Income									67,200	63,400	60,600
Noninterest expense									268,200	294,200	321,300
Income (loss) before income taxes									258,100	199,200	203,500
Average Loans	9,381,000				8,832,000				9,381,000	8,832,000	8,530,000
NBA [Member]
Segment Reporting Information [Line Items]
Net interest income									196,700	181,800	181,100
Provision for loan losses									(3,100)	7,900	(21,500)
Deposits	(4,609,000)				(4,369,000)				(4,609,000)	(4,369,000)	(4,133,000)
Net interest income after provision for loan losses									199,800	173,900	202,600
Noninterest Income									39,700	36,100	33,500
Noninterest expense									129,900	132,700	145,100
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest									109,600	77,300	91,000
Average Loans	$ 4,292,000				3,909,000				$ 4,292,000	3,909,000	3,750,000
Number of Branches | Branches	58								58
NSB [Member]
Segment Reporting Information [Line Items]
Net interest income									$ 124,800	125,300	125,400
Provision for loan losses									(28,400)	(28,300)	(20,900)
Deposits	$ (4,243,000)				(4,035,000)				(4,243,000)	(4,035,000)	(3,690,000)
Net interest income after provision for loan losses									153,200	153,600	146,300
Noninterest Income									39,400	36,300	34,900
Noninterest expense									123,500	131,300	132,700
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest									69,100	58,600	48,500
Average Loans	$ 2,344,000				2,285,000				$ 2,344,000	2,285,000	2,421,000
Number of Branches | Branches	50								50
Vectra [Member]
Segment Reporting Information [Line Items]
Net interest income									$ 123,100	117,200	114,000
Provision for loan losses									(7,900)	4,700	(8,400)
Deposits	$ (2,842,000)				(2,889,000)				(2,842,000)	(2,889,000)	(2,591,000)
Net interest income after provision for loan losses									131,000	112,500	122,400
Noninterest Income									22,800	21,300	22,300
Noninterest expense									87,300	97,600	98,300
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest									66,500	36,200	46,400
Average Loans	2,528,000				2,468,000				2,528,000	2,468,000	2,320,000
TCBW [Member]
Segment Reporting Information [Line Items]
Net interest income									39,500	34,600	34,600
Provision for loan losses									(200)	(2,900)	(900)
Deposits	(1,161,000)				(986,000)				(1,161,000)	(986,000)	(816,000)
Net interest income after provision for loan losses									39,700	37,500	35,500
Noninterest Income									4,600	4,100	4,100
Noninterest expense									18,600	16,500	33,400
Income (loss) before income taxes									25,700	25,100	6,200
Average Loans	$ 870,000				704,000				$ 870,000	704,000	713,000
Number of Branches | Branches	1								1
Consolidated Company [Member]
Segment Reporting Information [Line Items]
Net interest income									$ 1,867,400	1,715,300	1,680,000
Provision for loan losses									92,800	40,000	(98,100)
Deposits	$ (53,236,000)				(50,374,000)				(53,236,000)	(50,374,000)	(47,848,000)
Net interest income after provision for loan losses									1,774,600	1,675,300	1,778,100
Noninterest Income									515,600	357,200	492,700
Noninterest expense									1,585,300	1,580,600	1,649,400
Income (loss) before income taxes									704,900	451,900	621,400
Average Loans	$ 42,649,000				40,650,000				$ 42,649,000	40,650,000	40,064,000
The Commerce Bank Of Oregon [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	1								1
Utah [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	98								98
Idaho [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	23								23
WYOMING | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	1								1
Colorado [Member] | Vectra [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	36								36
New Mexico [Member] | Vectra [Member]
Segment Reporting Information [Line Items]
Number of Branches | Branches	1								1
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Net interest income									$ (179,300)	(259,500)	(314,400)
Provision for loan losses									100	0	0
Deposits	$ (724,000)				(335,000)				(724,000)	(335,000)	(794,000)
Net interest income after provision for loan losses									(179,400)	(259,500)	(314,400)
Noninterest Income									70,800	57,300	66,800
Noninterest expense									248,200	104,900	121,400
Income (loss) before income taxes									(356,800)	(421,700)	(369,000)
Average Loans	$ 117,000				$ 105,000				$ 117,000	$ 105,000	$ 81,000