Operating Segment Information (Details) (USD $)	3 Months Ended
Mar. 31, 2015 Banks	Mar. 31, 2014
Segment Reporting Information [Line Items]
Net interest income	$ 417,346,000us-gaap_InterestIncomeExpenseNet	$ 416,471,000us-gaap_InterestIncomeExpenseNet
Provision for loan losses	(1,494,000)us-gaap_ProvisionForLoanAndLeaseLosses	(610,000)us-gaap_ProvisionForLoanAndLeaseLosses
Net interest income after provision for loan losses	418,840,000	417,081,000
Other noninterest income	922,000	2,524,000
Noninterest expense	397,461,000us-gaap_NoninterestExpense	398,063,000us-gaap_NoninterestExpense
Income before income taxes	143,201,000	157,331,000
Income Tax Expense (Benefit)	51,176,000us-gaap_IncomeTaxExpenseBenefit	56,121,000us-gaap_IncomeTaxExpenseBenefit
Net income	92,025,000us-gaap_ProfitLoss	101,210,000us-gaap_ProfitLoss
Number of community/regional banks operating in distinct geographical areas	8
Zions Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	141,100,000	142,500,000
Provision for loan losses	(4,600,000)	(8,700,000)
Net interest income after provision for loan losses	145,700,000	151,200,000
Other noninterest income	46,800,000	44,000,000
Noninterest expense	127,400,000	121,500,000
Income before income taxes	65,100,000	73,700,000
Income Tax Expense (Benefit)	23,400,000	26,800,000
Net income	41,700,000	46,900,000
Net Income (Loss) Attributable to Noncontrolling Interest	500,000	0
Net income (loss) applicable to controlling interest	41,200,000	46,900,000
Total assets	18,573,000,000	18,275,000,000
Average cash and due from banks	297,000,000	339,000,000
Average money market investments	2,968,000,000	3,546,000,000
Average Securities	2,468,000,000	1,596,000,000
Total loans	12,180,000,000	12,247,000,000
Total deposits	16,160,000,000	15,980,000,000
Preferred equity	280,000,000	280,000,000
Common equity	1,633,000,000	1,538,000,000
Noncontrolling interests	11,000,000	0
Total shareholders' equity	1,924,000,000	1,818,000,000
CB&T [Member]
Segment Reporting Information [Line Items]
Net interest income	96,700,000	94,700,000
Provision for loan losses	11,100,000	16,900,000
Net interest income after provision for loan losses	85,600,000	77,800,000
Other noninterest income	34,000,000	32,000,000
Noninterest expense	94,000,000	87,000,000
Income before income taxes	25,600,000	22,800,000
Income Tax Expense (Benefit)	8,500,000	7,300,000
Net income	17,100,000	15,500,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	17,100,000	15,500,000
Total assets	13,964,000,000	13,467,000,000
Average cash and due from banks	183,000,000	322,000,000
Average money market investments	2,046,000,000	2,503,000,000
Average Securities	285,000,000	242,000,000
Total loans	10,276,000,000	9,362,000,000
Total deposits	11,478,000,000	11,099,000,000
Preferred equity	226,000,000	153,000,000
Common equity	1,940,000,000	1,849,000,000
Noncontrolling interests	0	0
Total shareholders' equity	2,166,000,000	2,002,000,000
Number of branches	94
Amegy [Member]
Segment Reporting Information [Line Items]
Net interest income	95,700,000	109,200,000
Provision for loan losses	(4,100,000)	(2,100,000)
Net interest income after provision for loan losses	99,800,000	111,300,000
Other noninterest income	16,700,000	5,800,000
Noninterest expense	74,400,000	85,300,000
Income before income taxes	42,100,000	31,800,000
Income Tax Expense (Benefit)	16,400,000	12,100,000
Net income	25,700,000	19,700,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	25,700,000	19,700,000
Total assets	11,368,000,000	10,889,000,000
Average cash and due from banks	90,000,000	166,000,000
Average money market investments	1,659,000,000	1,129,000,000
Average Securities	337,000,000	327,000,000
Total loans	8,502,000,000	8,538,000,000
Total deposits	9,701,000,000	9,273,000,000
Preferred equity	162,000,000	162,000,000
Common equity	1,394,000,000	1,350,000,000
Noncontrolling interests	0	0
Total shareholders' equity	1,556,000,000	1,512,000,000
Number of branches	80
NBA [Member]
Segment Reporting Information [Line Items]
Net interest income	39,000,000	40,300,000
Provision for loan losses	700,000	(3,000,000)
Net interest income after provision for loan losses	38,300,000	43,300,000
Other noninterest income	8,500,000	8,300,000
Noninterest expense	36,900,000	37,300,000
Income before income taxes	9,900,000	14,300,000
Income Tax Expense (Benefit)	3,400,000	5,200,000
Net income	6,500,000	9,100,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	6,500,000	9,100,000
Total assets	4,825,000,000	4,612,000,000
Average cash and due from banks	49,000,000	72,000,000
Average money market investments	396,000,000	289,000,000
Average Securities	412,000,000	365,000,000
Total loans	3,764,000,000	3,696,000,000
Total deposits	4,178,000,000	3,952,000,000
Preferred equity	85,000,000	120,000,000
Common equity	485,000,000	422,000,000
Noncontrolling interests	0	0
Total shareholders' equity	570,000,000	542,000,000
Number of branches	66
NSB [Member]
Segment Reporting Information [Line Items]
Net interest income	28,000,000	27,900,000
Provision for loan losses	(8,700,000)	(2,600,000)
Net interest income after provision for loan losses	36,700,000	30,500,000
Other noninterest income	9,000,000	4,900,000
Noninterest expense	32,100,000	32,100,000
Income before income taxes	13,600,000	3,300,000
Income Tax Expense (Benefit)	4,600,000	1,000,000
Net income	9,000,000	2,300,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	9,000,000	2,300,000
Total assets	4,164,000,000	3,991,000,000
Average cash and due from banks	71,000,000	88,000,000
Average money market investments	734,000,000	700,000,000
Average Securities	840,000,000	781,000,000
Total loans	2,384,000,000	2,306,000,000
Total deposits	3,755,000,000	3,598,000,000
Preferred equity	50,000,000	50,000,000
Common equity	332,000,000	318,000,000
Noncontrolling interests	0	0
Total shareholders' equity	382,000,000	368,000,000
Number of branches	50
Vectra [Member]
Segment Reporting Information [Line Items]
Net interest income	25,700,000	25,300,000
Provision for loan losses	3,800,000	(1,800,000)
Net interest income after provision for loan losses	21,900,000	27,100,000
Other noninterest income	5,000,000	3,800,000
Noninterest expense	23,900,000	25,300,000
Income before income taxes	3,000,000	5,600,000
Income Tax Expense (Benefit)	700,000	1,800,000
Net income	2,300,000	3,800,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	2,300,000	3,800,000
Total assets	2,977,000,000	2,569,000,000
Average cash and due from banks	29,000,000	47,000,000
Average money market investments	339,000,000	14,000,000
Average Securities	191,000,000	164,000,000
Total loans	2,358,000,000	2,280,000,000
Total deposits	2,568,000,000	2,168,000,000
Preferred equity	25,000,000	70,000,000
Common equity	317,000,000	247,000,000
Noncontrolling interests	0	0
Total shareholders' equity	342,000,000	317,000,000
TCBW [Member]
Segment Reporting Information [Line Items]
Net interest income	6,700,000	7,000,000
Provision for loan losses	100,000	700,000
Net interest income after provision for loan losses	6,600,000	6,300,000
Other noninterest income	900,000	(1,000,000)
Noninterest expense	6,900,000	4,500,000
Income before income taxes	600,000	800,000
Income Tax Expense (Benefit)	200,000	300,000
Net income	400,000	500,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	400,000	500,000
Total assets	896,000,000	873,000,000
Average cash and due from banks	29,000,000	21,000,000
Average money market investments	119,000,000	118,000,000
Average Securities	71,000,000	90,000,000
Total loans	661,000,000	631,000,000
Total deposits	766,000,000	742,000,000
Preferred equity	3,000,000	3,000,000
Common equity	90,000,000	88,000,000
Noncontrolling interests	0	0
Total shareholders' equity	93,000,000	91,000,000
Number of branches	1
Other Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	(15,500,000)	(30,400,000)
Provision for loan losses	200,000	0
Net interest income after provision for loan losses	(15,700,000)	(30,400,000)
Other noninterest income	900,000	40,500,000
Noninterest expense	1,900,000	5,100,000
Income before income taxes	(16,700,000)	5,000,000
Income Tax Expense (Benefit)	(6,000,000)	1,600,000
Net income	(10,700,000)	3,400,000
Net Income (Loss) Attributable to Noncontrolling Interest	(500,000)	0
Net income (loss) applicable to controlling interest	(10,200,000)	3,400,000
Total assets	51,000,000	758,000,000
Average cash and due from banks	(4,000,000)	(17,000,000)
Average money market investments	(248,000,000)	(159,000,000)
Average Securities	179,000,000	552,000,000
Total loans	54,000,000	65,000,000
Total deposits	(1,122,000,000)	(1,032,000,000)
Preferred equity	173,000,000	166,000,000
Common equity	214,000,000	(217,000,000)
Noncontrolling interests	(11,000,000)	0
Total shareholders' equity	376,000,000	(51,000,000)
Consolidated Company [Member]
Segment Reporting Information [Line Items]
Net interest income	417,400,000	416,500,000
Provision for loan losses	(1,500,000)	(600,000)
Net interest income after provision for loan losses	418,900,000	417,100,000
Other noninterest income	121,800,000	138,300,000
Noninterest expense	397,500,000	398,100,000
Income before income taxes	143,200,000	157,300,000
Income Tax Expense (Benefit)	51,200,000	56,100,000
Net income	92,000,000	101,200,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0
Net income (loss) applicable to controlling interest	92,000,000	101,200,000
Total assets	56,818,000,000	55,434,000,000
Average cash and due from banks	744,000,000	1,038,000,000
Average money market investments	8,013,000,000	8,140,000,000
Average Securities	4,783,000,000	4,117,000,000
Total loans	40,179,000,000	39,125,000,000
Total deposits	47,484,000,000	45,780,000,000
Preferred equity	1,004,000,000	1,004,000,000
Common equity	6,405,000,000	5,595,000,000
Noncontrolling interests	0	0
Total shareholders' equity	$ 7,409,000,000	$ 6,599,000,000
TCBO [Member]
Segment Reporting Information [Line Items]
Number of branches	1
Utah [Member] \| Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches	100
Idaho [Member] \| Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches	25
WYOMING \| Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches	1
Colorado [Member] \| Vectra [Member]
Segment Reporting Information [Line Items]
Number of branches	36
New Mexico [Member] \| Vectra [Member]
Segment Reporting Information [Line Items]
Number of branches	1

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