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