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Operating Segments (Summary of Operating Results by Segment) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 686,934,000us-gaap_InterestIncomeExpenseNet		$ 620,555,000us-gaap_InterestIncomeExpenseNet		$ 604,861,000us-gaap_InterestIncomeExpenseNet
Provision for loan losses	16,314,000us-gaap_ProvisionForLoanAndLeaseLosses		20,582,000us-gaap_ProvisionForLoanAndLeaseLosses		10,080,000us-gaap_ProvisionForLoanAndLeaseLosses
Non-interest income	320,144,000us-gaap_NoninterestIncome		302,818,000us-gaap_NoninterestIncome		288,787,000us-gaap_NoninterestIncome
Non-interest expense	654,740,000us-gaap_NoninterestExpense		611,910,000us-gaap_NoninterestExpense		575,093,000us-gaap_NoninterestExpense
Income (loss) before income taxes	336,024,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments		290,881,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments		308,475,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Income tax expense (benefit)	58,047,000us-gaap_IncomeTaxExpenseBenefit		53,015,000us-gaap_IncomeTaxExpenseBenefit		70,523,000us-gaap_IncomeTaxExpenseBenefit
Net income	277,977,000us-gaap_NetIncomeLoss		237,866,000us-gaap_NetIncomeLoss		237,952,000us-gaap_NetIncomeLoss
Preferred stock dividends	8,063,000us-gaap_PreferredStockDividendsAndOtherAdjustments		6,719,000us-gaap_PreferredStockDividendsAndOtherAdjustments		0us-gaap_PreferredStockDividendsAndOtherAdjustments
Net income available to common shareholders	269,914,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic		231,147,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic		237,952,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Revenues from (expenses to) external customers	1,007,078,000us-gaap_Revenues		923,373,000us-gaap_Revenues		893,648,000us-gaap_Revenues
Average assets	25,768,000,000cfr_SegmentReportingAverageAssets	[1]	22,752,000,000cfr_SegmentReportingAverageAssets	[1]	20,827,000,000cfr_SegmentReportingAverageAssets	[1]
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	683,579,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		621,333,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		605,330,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Provision for loan losses	16,312,000us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		20,585,000us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		10,078,000us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Non-interest income	193,883,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		190,767,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		188,440,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Non-interest expense	549,812,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		513,909,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		485,302,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Income (loss) before income taxes	311,338,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		277,606,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		298,390,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Income tax expense (benefit)	51,881,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		50,823,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		69,078,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Net income	259,457,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		226,783,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		229,312,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Preferred stock dividends	0us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		0us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Net income available to common shareholders	259,457,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		226,783,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Revenues from (expenses to) external customers	877,462,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		812,100,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember		793,770,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember
Average assets	25,734,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember	[1]	22,709,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember	[1]	20,783,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_BankingMember	[1]
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	6,734,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		6,586,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		8,013,000us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Provision for loan losses	2,000us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		(3,000)us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		2,000us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Non-interest income	122,261,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		107,759,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		96,577,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Non-interest expense	96,330,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		90,132,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		82,744,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Income (loss) before income taxes	32,663,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		24,216,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		21,844,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Income tax expense (benefit)	11,431,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		8,563,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		7,646,000us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Net income	21,232,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		15,653,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		14,198,000us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Preferred stock dividends	0us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		0us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Net income available to common shareholders	21,232,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		15,653,000us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Revenues from (expenses to) external customers	128,995,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		114,345,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember		104,590,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember
Average assets	32,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember	[1]	31,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember	[1]	29,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_FrostWealthAdvisorsMember	[1]
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(3,379,000)us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(7,364,000)us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(8,482,000)us-gaap_InterestIncomeExpenseNet / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Provision for loan losses	0us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		0us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		0us-gaap_ProvisionForLoanAndLeaseLosses / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Non-interest income	4,000,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		4,292,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		3,770,000us-gaap_NoninterestIncome / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Non-interest expense	8,598,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		7,869,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		7,047,000us-gaap_NoninterestExpense / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Income (loss) before income taxes	(7,977,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(10,941,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(11,759,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Income tax expense (benefit)	(5,265,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(6,371,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(6,201,000)us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Net income	(2,712,000)us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(4,570,000)us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(5,558,000)us-gaap_NetIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Preferred stock dividends	8,063,000us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		6,719,000us-gaap_PreferredStockDividendsAndOtherAdjustments / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Net income available to common shareholders	(10,775,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(11,289,000)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Revenues from (expenses to) external customers	621,000us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(3,072,000)us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember		(4,712,000)us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember
Average assets	$ 2,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember	[1]	$ 12,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember	[1]	$ 15,000,000cfr_SegmentReportingAverageAssets / us-gaap_StatementBusinessSegmentsAxis = cfr_NonBanksMember	[1]
[1] Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.5 billion, $29.0 billion and $26.2 billion at December 31, 2014, 2013 and 2012.

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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