Operating Segment Information (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012 Banks	Jun. 30, 2011	Jun. 30, 2012 Banks	Jun. 30, 2011
Segment Reporting Information [Line Items]
Net interest income	$ 431,987,000	$ 416,172,000	$ 874,286,000	$ 840,028,000
Provision for loan losses	10,853,000	1,330,000	26,517,000	61,330,000
Net interest income after provision for loan losses	421,134,000	414,842,000	847,769,000	778,698,000
Net impairment losses on investment securities	(7,308,000)	(5,158,000)	(17,517,000)	(8,263,000)
Other noninterest income	2,280,000	3,896,000	6,325,000	24,862,000
Noninterest expense	401,656,000	416,256,000	794,028,000	824,631,000
Income (loss) before income taxes	142,500,000	126,935,000	283,762,000	216,559,000
Income tax expense (benefit)	51,036,000	54,325,000	102,895,000	91,358,000
Net income	91,464,000	72,610,000	180,867,000	125,201,000
Net income (loss) applicable to noncontrolling interests	(273,000)	(265,000)	(546,000)	(491,000)
Net income (loss) applicable to controlling interest	91,737,000	72,875,000	181,413,000	125,692,000
Preferred stock dividends			(72,614,000)	(71,251,000)
Net earnings (loss) applicable to common shareholders	55,215,000	29,038,000	80,704,000	43,805,000
Number of community/regional banks operating in distinct geographical areas	8		8
Zions Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	171,600,000	176,400,000	344,200,000	349,000,000
Provision for loan losses	20,400,000	21,600,000	60,900,000	60,600,000
Net interest income after provision for loan losses	151,200,000	154,800,000	283,300,000	288,400,000
Net impairment losses on investment securities	(200,000)	0	(200,000)	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	45,600,000	49,600,000	100,900,000	99,100,000
Noninterest expense	125,500,000	137,200,000	247,500,000	265,600,000
Income (loss) before income taxes	71,100,000	67,200,000	136,500,000	121,900,000
Income tax expense (benefit)	25,200,000	23,000,000	48,100,000	41,200,000
Net income	45,900,000	44,200,000	88,400,000	80,700,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	45,900,000	44,200,000	88,400,000	80,700,000
Preferred stock dividends	(6,000,000)	0	(12,000,000)	0
Net earnings (loss) applicable to common shareholders	39,900,000	44,200,000	76,400,000	80,700,000
Total assets	17,330,000,000	16,149,000,000	17,293,000,000	16,158,000,000
Total loans	12,402,000,000	12,799,000,000	12,468,000,000	12,814,000,000
Total deposits	14,814,000,000	13,621,000,000	14,759,000,000	13,557,000,000
Preferred equity	480,000,000	480,000,000	480,000,000	480,000,000
Common equity	1,430,000,000	1,285,000,000	1,408,000,000	1,289,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	1,910,000,000	1,765,000,000	1,888,000,000	1,769,000,000
CB&T [Member]
Segment Reporting Information [Line Items]
Net interest income	117,900,000	128,400,000	235,700,000	257,100,000
Provision for loan losses	(3,800,000)	(5,800,000)	(6,700,000)	5,400,000
Net interest income after provision for loan losses	121,700,000	134,200,000	242,400,000	251,700,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	(9,200,000)	(13,500,000)
Other noninterest income	18,400,000	23,800,000	36,900,000	62,200,000
Noninterest expense	84,400,000	93,100,000	165,600,000	183,400,000
Income (loss) before income taxes	55,700,000	64,900,000	104,500,000	117,000,000
Income tax expense (benefit)	22,200,000	26,000,000	41,300,000	46,500,000
Net income	33,500,000	38,900,000	63,200,000	70,500,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	33,500,000	38,900,000	63,200,000	70,500,000
Preferred stock dividends	(3,300,000)	0	(6,600,000)	0
Net earnings (loss) applicable to common shareholders	30,200,000	38,900,000	56,600,000	70,500,000
Total assets	10,880,000,000	10,804,000,000	10,857,000,000	10,785,000,000
Total loans	8,350,000,000	8,285,000,000	8,347,000,000	8,316,000,000
Total deposits	9,219,000,000	9,221,000,000	9,166,000,000	9,217,000,000
Preferred equity	248,000,000	262,000,000	255,000,000	262,000,000
Common equity	1,291,000,000	1,224,000,000	1,286,000,000	1,207,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	1,539,000,000	1,486,000,000	1,541,000,000	1,469,000,000
Number of branches	102		102
Amegy [Member]
Segment Reporting Information [Line Items]
Net interest income	90,400,000	98,300,000	184,700,000	191,300,000
Provision for loan losses	(8,900,000)	(200,000)	(32,200,000)	3,100,000
Net interest income after provision for loan losses	99,300,000	98,500,000	216,900,000	188,200,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	45,300,000	39,300,000	78,900,000	73,300,000
Noninterest expense	86,800,000	84,100,000	168,800,000	164,000,000
Income (loss) before income taxes	57,800,000	53,700,000	127,000,000	97,500,000
Income tax expense (benefit)	18,800,000	17,700,000	42,100,000	31,900,000
Net income	39,000,000	36,000,000	84,900,000	65,600,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	39,000,000	36,000,000	84,900,000	65,600,000
Preferred stock dividends	(6,100,000)	0	(12,200,000)	0
Net earnings (loss) applicable to common shareholders	32,900,000	36,000,000	72,700,000	65,600,000
Total assets	12,081,000,000	11,235,000,000	12,058,000,000	11,228,000,000
Total loans	7,909,000,000	7,794,000,000	7,892,000,000	7,683,000,000
Total deposits	9,595,000,000	8,712,000,000	9,534,000,000	8,706,000,000
Preferred equity	410,000,000	488,000,000	449,000,000	488,000,000
Common equity	1,661,000,000	1,544,000,000	1,653,000,000	1,527,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	2,071,000,000	2,032,000,000	2,102,000,000	2,015,000,000
Number of branches	83		83
NBA [Member]
Segment Reporting Information [Line Items]
Net interest income	41,400,000	43,300,000	83,500,000	86,400,000
Provision for loan losses	2,500,000	1,800,000	9,000,000	2,500,000
Net interest income after provision for loan losses	38,900,000	41,500,000	74,500,000	83,900,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	7,800,000	9,500,000	15,500,000	18,000,000
Noninterest expense	38,000,000	37,000,000	75,900,000	82,100,000
Income (loss) before income taxes	8,700,000	14,000,000	14,100,000	19,800,000
Income tax expense (benefit)	3,400,000	5,500,000	5,500,000	7,800,000
Net income	5,300,000	8,500,000	8,600,000	12,000,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	5,300,000	8,500,000	8,600,000	12,000,000
Preferred stock dividends	(1,500,000)	0	(1,500,000)	0
Net earnings (loss) applicable to common shareholders	3,800,000	8,500,000	7,100,000	12,000,000
Total assets	4,457,000,000	4,482,000,000	4,462,000,000	4,455,000,000
Total loans	3,280,000,000	3,305,000,000	3,280,000,000	3,289,000,000
Total deposits	3,721,000,000	3,745,000,000	3,715,000,000	3,728,000,000
Preferred equity	275,000,000	305,000,000	290,000,000	305,000,000
Common equity	358,000,000	332,000,000	355,000,000	328,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	633,000,000	637,000,000	645,000,000	633,000,000
Number of branches	74		74
NSB [Member]
Segment Reporting Information [Line Items]
Net interest income	31,000,000	35,300,000	62,200,000	68,400,000
Provision for loan losses	(1,600,000)	(18,200,000)	(8,300,000)	(17,400,000)
Net interest income after provision for loan losses	32,600,000	53,500,000	70,500,000	85,800,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	8,500,000	10,100,000	16,400,000	18,700,000
Noninterest expense	34,300,000	35,700,000	69,600,000	70,300,000
Income (loss) before income taxes	6,800,000	27,900,000	17,300,000	34,200,000
Income tax expense (benefit)	2,400,000	9,800,000	6,000,000	11,900,000
Net income	4,400,000	18,100,000	11,300,000	22,300,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	4,400,000	18,100,000	11,300,000	22,300,000
Preferred stock dividends	0	0	0	0
Net earnings (loss) applicable to common shareholders	4,400,000	18,100,000	11,300,000	22,300,000
Total assets	4,171,000,000	4,169,000,000	4,148,000,000	4,134,000,000
Total loans	2,169,000,000	2,408,000,000	2,186,000,000	2,416,000,000
Total deposits	3,626,000,000	3,548,000,000	3,597,000,000	3,518,000,000
Preferred equity	242,000,000	360,000,000	251,000,000	360,000,000
Common equity	279,000,000	235,000,000	277,000,000	231,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	521,000,000	595,000,000	528,000,000	591,000,000
Number of branches	53		53
Vectra [Member]
Segment Reporting Information [Line Items]
Net interest income	28,600,000	26,000,000	54,300,000	51,800,000
Provision for loan losses	1,400,000	(1,200,000)	2,400,000	1,900,000
Net interest income after provision for loan losses	27,200,000	27,200,000	51,900,000	49,900,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	5,600,000	5,300,000	11,000,000	10,800,000
Noninterest expense	24,700,000	26,300,000	49,600,000	51,000,000
Income (loss) before income taxes	8,100,000	6,200,000	13,300,000	9,700,000
Income tax expense (benefit)	2,700,000	2,100,000	4,300,000	3,100,000
Net income	5,400,000	4,100,000	9,000,000	6,600,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	5,400,000	4,100,000	9,000,000	6,600,000
Preferred stock dividends	0	0	0	0
Net earnings (loss) applicable to common shareholders	5,400,000	4,100,000	9,000,000	6,600,000
Total assets	2,380,000,000	2,245,000,000	2,372,000,000	2,249,000,000
Total loans	1,993,000,000	1,791,000,000	1,963,000,000	1,787,000,000
Total deposits	2,029,000,000	1,873,000,000	2,028,000,000	1,873,000,000
Preferred equity	70,000,000	70,000,000	70,000,000	70,000,000
Common equity	208,000,000	204,000,000	205,000,000	203,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	278,000,000	274,000,000	275,000,000	273,000,000
TCBW [Member]
Segment Reporting Information [Line Items]
Net interest income	7,100,000	7,600,000	14,500,000	15,200,000
Provision for loan losses	800,000	3,200,000	1,400,000	5,100,000
Net interest income after provision for loan losses	6,300,000	4,400,000	13,100,000	10,100,000
Net impairment losses on investment securities	0	0	0	0
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	700,000	800,000	1,300,000	1,300,000
Noninterest expense	4,300,000	3,900,000	9,000,000	8,400,000
Income (loss) before income taxes	2,700,000	1,300,000	5,400,000	3,000,000
Income tax expense (benefit)	900,000	400,000	1,800,000	900,000
Net income	1,800,000	900,000	3,600,000	2,100,000
Net income (loss) applicable to noncontrolling interests	0	0	0	0
Net income (loss) applicable to controlling interest	1,800,000	900,000	3,600,000	2,100,000
Preferred stock dividends	(200,000)	0	(200,000)	0
Net earnings (loss) applicable to common shareholders	1,600,000	900,000	3,400,000	2,100,000
Total assets	871,000,000	852,000,000	884,000,000	852,000,000
Total loans	557,000,000	586,000,000	556,000,000	577,000,000
Total deposits	721,000,000	671,000,000	734,000,000	670,000,000
Preferred equity	13,000,000	15,000,000	14,000,000	15,000,000
Common equity	78,000,000	72,000,000	77,000,000	71,000,000
Noncontrolling interests	0	0	0	0
Total shareholders' equity	91,000,000	87,000,000	91,000,000	86,000,000
Number of branches	1		1
Other Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	(56,000,000)	(99,100,000)	(104,800,000)	(179,200,000)
Provision for loan losses	100,000	100,000	0	100,000
Net interest income after provision for loan losses	(56,100,000)	(99,200,000)	(104,800,000)	(179,300,000)
Net impairment losses on investment securities	(7,100,000)	(5,200,000)	(17,300,000)	(8,300,000)
Loss on sale of investment securities to Parent	0	0	9,200,000	13,500,000
Other noninterest income	(1,600,000)	(4,900,000)	(13,400,000)	(12,600,000)
Noninterest expense	3,600,000	(1,000,000)	8,000,000	(200,000)
Income (loss) before income taxes	(68,400,000)	(108,300,000)	(134,300,000)	(186,500,000)
Income tax expense (benefit)	(24,600,000)	(30,200,000)	(46,200,000)	(51,900,000)
Net income	(43,800,000)	(78,100,000)	(88,100,000)	(134,600,000)
Net income (loss) applicable to noncontrolling interests	(200,000)	(200,000)	(500,000)	(500,000)
Net income (loss) applicable to controlling interest	(43,600,000)	(77,900,000)	(87,600,000)	(134,100,000)
Preferred stock dividends	(19,400,000)	(43,800,000)	(68,200,000)	(81,900,000)
Net earnings (loss) applicable to common shareholders	(63,000,000)	(121,700,000)	(155,800,000)	(216,000,000)
Total assets	720,000,000	1,056,000,000	661,000,000	988,000,000
Total loans	69,000,000	(128,000,000)	68,000,000	(128,000,000)
Total deposits	(783,000,000)	(506,000,000)	(876,000,000)	(532,000,000)
Preferred equity	93,000,000	266,000,000	284,000,000	182,000,000
Common equity	(592,000,000)	(298,000,000)	(582,000,000)	(236,000,000)
Noncontrolling interests	(2,000,000)	(1,000,000)	(2,000,000)	(1,000,000)
Total shareholders' equity	(501,000,000)	(33,000,000)	(300,000,000)	(55,000,000)
Consolidated Company [Member]
Segment Reporting Information [Line Items]
Net interest income	432,000,000	416,200,000	874,300,000	840,000,000
Provision for loan losses	10,900,000	1,300,000	26,500,000	61,300,000
Net interest income after provision for loan losses	421,100,000	414,900,000	847,800,000	778,700,000
Net impairment losses on investment securities	(7,300,000)	(5,200,000)	(17,500,000)	(8,300,000)
Loss on sale of investment securities to Parent	0	0	0	0
Other noninterest income	130,300,000	133,500,000	247,500,000	270,800,000
Noninterest expense	401,600,000	416,300,000	794,000,000	824,600,000
Income (loss) before income taxes	142,500,000	126,900,000	283,800,000	216,600,000
Income tax expense (benefit)	51,000,000	54,300,000	102,900,000	91,400,000
Net income	91,500,000	72,600,000	180,900,000	125,200,000
Net income (loss) applicable to noncontrolling interests	(200,000)	(200,000)	(500,000)	(500,000)
Net income (loss) applicable to controlling interest	91,700,000	72,800,000	181,400,000	125,700,000
Preferred stock dividends	(36,500,000)	(43,800,000)	(100,700,000)	(81,900,000)
Net earnings (loss) applicable to common shareholders	55,200,000	29,000,000	80,700,000	43,800,000
Total assets	52,890,000,000	50,992,000,000	52,735,000,000	50,849,000,000
Total loans	36,729,000,000	36,840,000,000	36,760,000,000	36,754,000,000
Total deposits	42,942,000,000	40,885,000,000	42,657,000,000	40,737,000,000
Preferred equity	1,831,000,000	2,246,000,000	2,093,000,000	2,162,000,000
Common equity	4,713,000,000	4,598,000,000	4,679,000,000	4,620,000,000
Noncontrolling interests	(2,000,000)	(1,000,000)	(2,000,000)	(1,000,000)
Total shareholders' equity	$ 6,542,000,000	$ 6,843,000,000	$ 6,770,000,000	$ 6,781,000,000
TCBO [Member]
Segment Reporting Information [Line Items]
Number of branches	1		1
Utah [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches	105		105
Idaho [Member] | Zions Bank [Member]
Segment Reporting Information [Line Items]
Number of branches	26		26
Colorado [Member] | Vectra [Member]
Segment Reporting Information [Line Items]
Number of branches	37		37
New Mexico [Member] | Vectra [Member]
Segment Reporting Information [Line Items]
Number of branches	1		1