Operating Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) Branches Banks	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) Branches Banks	Jun. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Realized Losses on Sales of CDOs	$ 137,000
Net interest income	423,704	$ 416,284	$ 841,050	$ 832,754
Provision for loan losses	566	(54,416)	(928)	(55,026)
Net interest income after provision for loan losses	423,138	470,700	841,978	887,780
Other noninterest income	5,693	703	6,615	3,227
Noninterest expense	404,100	406,027	801,561	804,090
Income before income taxes	19,459	189,522	162,660	346,853
Income Tax Expense (Benefit)	5,499	69,972	56,675	126,093
Net income	$ 13,960	119,550	$ 105,985	220,760
Number of community/regional banks operating in distinct geographical areas | Banks	7		7
Zions Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	$ 144,200	145,600	$ 285,300	288,100
Provision for loan losses	(8,400)	(15,400)	(13,000)	(24,100)
Net interest income after provision for loan losses	152,600	161,000	298,300	312,200
Other noninterest income	(6,600)	50,200	40,200	94,200
Noninterest expense	129,300	121,100	256,700	242,600
Income before income taxes	16,700	90,100	81,800	163,800
Income Tax Expense (Benefit)	4,600	33,200	28,000	60,000
Net income	12,100	56,900	53,800	103,800
Net Income (Loss) Attributable to Noncontrolling Interest	900	0	1,400	0
Net income (loss) applicable to controlling interest	11,200	56,900	52,400	103,800
Total assets	18,875,000	17,593,000	18,725,000	17,932,000
Average cash and due from banks	251,000	335,000	274,000	337,000
Average money market investments	2,970,000	2,679,000	2,969,000	3,110,000
Average Securities	2,794,000	1,747,000	2,632,000	1,672,000
Total loans	12,172,000	12,317,000	12,176,000	12,282,000
Total deposits	16,456,000	15,322,000	16,309,000	15,649,000
Preferred equity	280,000	280,000	280,000	280,000
Common equity	1,639,000	1,552,000	1,636,000	1,545,000
Noncontrolling interests	11,000	0	11,000	0
Total shareholders' equity	1,930,000	1,832,000	1,927,000	1,825,000
Amegy [Member]
Segment Reporting Information [Line Items]
Net interest income	95,000	95,400	191,700	190,100
Provision for loan losses	14,000	(7,500)	25,100	9,400
Net interest income after provision for loan losses	81,000	102,900	166,600	180,700
Other noninterest income	33,800	36,300	67,800	68,300
Noninterest expense	96,700	92,500	190,700	179,500
Income before income taxes	18,100	46,700	43,700	69,500
Income Tax Expense (Benefit)	5,200	15,900	13,700	23,200
Net income	12,900	30,800	30,000	46,300
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	12,900	30,800	30,000	46,300
Total assets	13,674,000	13,618,000	13,818,000	13,543,000
Average cash and due from banks	97,000	213,000	140,000	267,000
Average money market investments	1,980,000	2,435,000	2,013,000	2,469,000
Average Securities	281,000	260,000	283,000	251,000
Total loans	10,159,000	9,563,000	10,217,000	9,463,000
Total deposits	11,198,000	11,167,000	11,337,000	11,133,000
Preferred equity	226,000	227,000	226,000	190,000
Common equity	1,952,000	1,873,000	1,946,000	1,861,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	$ 2,178,000	2,100,000	$ 2,172,000	2,051,000
Number of branches | Branches	79		79
California Bank Trust [Member]
Segment Reporting Information [Line Items]
Net interest income	$ 98,700	103,700	$ 194,400	212,900
Provision for loan losses	(3,500)	(12,900)	(7,600)	(15,000)
Net interest income after provision for loan losses	102,200	116,600	202,000	227,900
Other noninterest income	21,200	13,800	37,900	19,600
Noninterest expense	79,400	82,400	153,800	167,700
Income before income taxes	44,000	48,000	86,100	79,800
Income Tax Expense (Benefit)	17,200	19,000	33,600	31,100
Net income	26,800	29,000	52,500	48,700
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	26,800	29,000	52,500	48,700
Total assets	11,515,000	11,044,000	11,442,000	10,967,000
Average cash and due from banks	86,000	156,000	88,000	161,000
Average money market investments	1,776,000	1,252,000	1,718,000	1,191,000
Average Securities	425,000	237,000	381,000	282,000
Total loans	8,472,000	8,655,000	8,487,000	8,597,000
Total deposits	9,864,000	9,394,000	9,783,000	9,334,000
Preferred equity	162,000	162,000	162,000	162,000
Common equity	1,406,000	1,368,000	1,400,000	1,359,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	$ 1,568,000	1,530,000	$ 1,562,000	1,521,000
Number of branches | Branches	94		94
NBA [Member]
Segment Reporting Information [Line Items]
Net interest income	$ 40,300	40,300	$ 79,300	80,600
Provision for loan losses	2,700	(8,000)	3,400	(11,000)
Net interest income after provision for loan losses	37,600	48,300	75,900	91,600
Other noninterest income	10,800	8,300	19,300	16,600
Noninterest expense	36,800	38,900	73,700	76,200
Income before income taxes	11,600	17,700	21,500	32,000
Income Tax Expense (Benefit)	4,000	6,600	7,400	11,800
Net income	7,600	11,100	14,100	20,200
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	7,600	11,100	14,100	20,200
Total assets	4,942,000	4,696,000	4,884,000	4,654,000
Average cash and due from banks	43,000	74,000	46,000	73,000
Average money market investments	402,000	412,000	399,000	351,000
Average Securities	450,000	371,000	431,000	368,000
Total loans	3,846,000	3,648,000	3,805,000	3,672,000
Total deposits	4,291,000	4,014,000	4,235,000	3,983,000
Preferred equity	85,000	98,000	85,000	109,000
Common equity	491,000	454,000	488,000	438,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	$ 576,000	552,000	$ 573,000	547,000
Number of branches | Branches	66		66
Nevada State Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	$ 28,300	28,300	$ 56,300	56,200
Provision for loan losses	(3,000)	(5,700)	(11,700)	(8,300)
Net interest income after provision for loan losses	31,300	34,000	68,000	64,500
Other noninterest income	8,400	8,900	17,400	13,800
Noninterest expense	33,600	34,000	65,700	66,100
Income before income taxes	6,100	8,900	19,700	12,200
Income Tax Expense (Benefit)	2,000	3,000	6,600	4,000
Net income	4,100	5,900	13,100	8,200
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	4,100	5,900	13,100	8,200
Total assets	4,311,000	4,073,000	4,238,000	4,032,000
Average cash and due from banks	75,000	82,000	73,000	85,000
Average money market investments	885,000	764,000	810,000	732,000
Average Securities	858,000	787,000	849,000	784,000
Total loans	2,358,000	2,318,000	2,371,000	2,312,000
Total deposits	3,902,000	3,676,000	3,829,000	3,637,000
Preferred equity	50,000	50,000	50,000	50,000
Common equity	332,000	324,000	332,000	321,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	$ 382,000	374,000	$ 382,000	371,000
Number of branches | Branches	50		50
Vectra Bank Colorado [Member]
Segment Reporting Information [Line Items]
Net interest income	$ 26,400	25,400	$ 52,100	50,700
Provision for loan losses	(400)	(4,500)	3,500	(6,300)
Net interest income after provision for loan losses	26,800	29,900	48,600	57,000
Other noninterest income	4,700	5,900	9,800	9,700
Noninterest expense	24,400	23,700	48,300	49,000
Income before income taxes	7,100	12,100	10,100	17,700
Income Tax Expense (Benefit)	2,400	4,300	3,100	6,100
Net income	4,700	7,800	7,000	11,600
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	4,700	7,800	7,000	11,600
Total assets	3,236,000	2,595,000	3,107,000	2,582,000
Average cash and due from banks	29,000	47,000	29,000	47,000
Average money market investments	522,000	20,000	431,000	17,000
Average Securities	225,000	158,000	208,000	161,000
Total loans	2,400,000	2,316,000	2,379,000	2,298,000
Total deposits	2,831,000	2,184,000	2,700,000	2,176,000
Preferred equity	25,000	42,000	25,000	56,000
Common equity	319,000	283,000	318,000	265,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	344,000	325,000	343,000	321,000
TCBW [Member]
Segment Reporting Information [Line Items]
Net interest income	7,700	8,000	15,100	15,700
Provision for loan losses	(800)	(400)	(600)	300
Net interest income after provision for loan losses	8,500	8,400	15,700	15,400
Other noninterest income	1,200	1,300	2,200	300
Noninterest expense	(1,500)	6,000	6,300	11,400
Income before income taxes	11,200	3,700	11,600	4,300
Income Tax Expense (Benefit)	3,900	1,300	4,000	1,500
Net income	7,300	2,400	7,600	2,800
Net Income (Loss) Attributable to Noncontrolling Interest	0	0	0	0
Net income (loss) applicable to controlling interest	7,300	2,400	7,600	2,800
Total assets	987,000	948,000	981,000	947,000
Average cash and due from banks	35,000	25,000	35,000	25,000
Average money market investments	142,000	104,000	135,000	113,000
Average Securities	79,000	82,000	80,000	87,000
Total loans	721,000	725,000	717,000	709,000
Total deposits	852,000	799,000	841,000	800,000
Preferred equity	3,000	3,000	3,000	3,000
Common equity	107,000	106,000	105,000	104,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	110,000	109,000	108,000	107,000
Other Segment [Member]
Segment Reporting Information [Line Items]
Net interest income	(16,900)	(30,400)	(33,100)	(61,500)
Provision for loan losses	0	0	0	0
Net interest income after provision for loan losses	(16,900)	(30,400)	(33,100)	(61,500)
Other noninterest income	(73,100)	200	(72,400)	40,700
Noninterest expense	5,400	7,400	6,300	11,600
Income before income taxes	(95,400)	(37,600)	(111,800)	(32,400)
Income Tax Expense (Benefit)	(33,900)	(13,300)	(39,700)	(11,600)
Net income	(61,500)	(24,300)	(72,100)	(20,800)
Net Income (Loss) Attributable to Noncontrolling Interest	(900)	0	(1,400)	0
Net income (loss) applicable to controlling interest	(60,600)	(24,300)	(70,700)	(20,800)
Total assets	(62,000)	469,000	(46,000)	577,000
Average cash and due from banks	(25,000)	(13,000)	(18,000)	(17,000)
Average money market investments	(262,000)	(162,000)	(260,000)	(163,000)
Average Securities	134,000	381,000	152,000	465,000
Total loans	3,000	2,000	3,000	2,000
Total deposits	(1,269,000)	(1,097,000)	(1,228,000)	(1,093,000)
Preferred equity	173,000	142,000	173,000	154,000
Common equity	247,000	(215,000)	224,000	(223,000)
Noncontrolling interests	(11,000)	0	(11,000)	0
Total shareholders' equity	409,000	(73,000)	386,000	(69,000)
Consolidated Company [Member]
Segment Reporting Information [Line Items]
Net interest income			841,100	832,800
Provision for loan losses			(900)	(55,000)
Net interest income after provision for loan losses			842,000	887,800
Other noninterest income			122,200	263,200
Noninterest expense			801,500	804,100
Income before income taxes			162,700	346,900
Income Tax Expense (Benefit)			56,700	126,100
Net income			106,000	220,800
Net Income (Loss) Attributable to Noncontrolling Interest			0	0
Net income (loss) applicable to controlling interest			106,000	220,800
Total assets			57,149,000	55,234,000
Average cash and due from banks			667,000	978,000
Average money market investments			8,215,000	7,820,000
Average Securities			5,016,000	4,070,000
Total loans			40,155,000	39,335,000
Total deposits			47,806,000	45,619,000
Preferred equity			1,004,000	1,004,000
Common equity			6,449,000	5,670,000
Noncontrolling interests			0	0
Total shareholders' equity			$ 7,453,000	$ 6,674,000
Consolidated Entities [Member]
Segment Reporting Information [Line Items]
Net interest income	423,700	416,300
Provision for loan losses	600	(54,400)
Net interest income after provision for loan losses	423,100	470,700
Other noninterest income	400	124,900
Noninterest expense	404,100	406,000
Income before income taxes	19,400	189,600
Income Tax Expense (Benefit)	5,400	70,000
Net income	14,000	119,600
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	14,000	119,600
Total assets	57,478,000	55,036,000
Average cash and due from banks	591,000	919,000
Average money market investments	8,415,000	7,504,000
Average Securities	5,246,000	4,023,000
Total loans	40,131,000	39,544,000
Total deposits	48,125,000	45,459,000
Preferred equity	1,004,000	1,004,000
Common equity	6,493,000	5,745,000
Noncontrolling interests	0	0
Total shareholders' equity	$ 7,497,000	$ 6,749,000
Utah [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	101		101
Idaho [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	25		25
WYOMING | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	1		1
Colorado [Member] | Vectra Bank Colorado [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	36		36
New Mexico [Member] | Vectra Bank Colorado [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	1		1
WASHINGTON | TCBW [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	1		1
OREGON | TCBW [Member]
Segment Reporting Information [Line Items]
Number of branches | Branches	1		1
Other Segment [Member]
Segment Reporting Information [Line Items]
Realized Losses on Sales of CDOs	$ 73,100
Vectra Bank Colorado [Member]
Segment Reporting Information [Line Items]
Realized Losses on Sales of CDOs	600
Nevada State Bank [Member]
Segment Reporting Information [Line Items]
Realized Losses on Sales of CDOs	600
Zions Bank [Member]
Segment Reporting Information [Line Items]
Realized Losses on Sales of CDOs	$ 62,500