v3.22.4
Regulatory Matters (Actual and Required Capital Ratios) (Detail) - USD ($)
$ in Thousands
Dec. 31, 2022
Dec. 31, 2021
Jan. 01, 2019
Cullen/Frost [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Common Equity Tier One to Risk-Weighted Assets, Actual, Capital Amount $ 3,751,200 $ 3,371,043  
Common Equity Tier One Risk-Based Capital Ratio, Actual 12.85% 13.13%  
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,042,876 $ 1,796,549  
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00% 7.00%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount $ 3,896,652 $ 3,516,495  
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio 13.35% 13.70%  
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,480,635 $ 2,181,523  
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 8.50% 8.50% 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 1,751,036 $ 1,539,899  
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 6.00% 6.00%  
Total Capital to Risk-Weighted Assets, Actual, Capital Amount $ 4,330,982 $ 3,966,244  
Total Capital to Risk-Weighted Assets, Actual, Ratio 14.84% 15.45% 8.00%
Capital Required for Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 3,064,313 $ 2,694,823  
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 10.50% 10.50% 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 2,918,394 $ 2,566,498  
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 10.00% 10.00%  
Leverage Ratio, Actual, Capital Amount $ 3,896,652 $ 3,516,495  
Leverage Ratio, Actual, Ratio 7.29% 7.34%  
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,136,680 $ 1,917,533  
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 4.00% 4.00% 4.00%
Frost Bank [Member]      
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]      
Common Equity Tier One to Risk-Weighted Assets, Actual, Capital Amount $ 3,789,056 $ 3,261,532  
Common Equity Tier One Risk-Based Capital Ratio, Actual 13.00% 12.72%  
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,040,388 $ 1,795,221  
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 7.00% 7.00% 7.00%
Common Equity Tier One Capital Required To Be Well Capitalized, Capital Amount $ 1,894,646 $ 1,666,991  
Common Equity Tier One Risk-Based Capital Ratio, Well Capitalized, Minimum 6.50% 6.50%  
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount $ 3,789,056 $ 3,261,532  
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio 13.00% 12.72%  
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,477,614 $ 2,179,911  
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 8.50% 8.50% 8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 2,331,872 $ 2,051,681  
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 8.00% 8.00%  
Total Capital to Risk-Weighted Assets, Actual, Capital Amount $ 4,023,386 $ 3,491,281  
Total Capital to Risk-Weighted Assets, Actual, Ratio 13.80% 13.61% 8.00%
Capital Required for Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 3,060,583 $ 2,692,831  
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 10.50% 10.50% 10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount $ 2,914,841 $ 2,564,601  
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio 10.00% 10.00%  
Leverage Ratio, Actual, Capital Amount $ 3,789,056 $ 3,261,532  
Leverage Ratio, Actual, Ratio 7.09% 6.80%  
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Plus Capital Conservation Buffer, Capital Amount $ 2,136,316 $ 1,917,679  
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Plus Capital Conservation Buffer, Ratio 4.00% 4.00% 4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount $ 2,670,395 $ 2,397,099  
Leverage Ratio, Required to be Considered Well Capitalized, Ratio 5.00% 5.00%