Capital and Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2019

Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]

Actual and Required Capital Ratios

The following table presents actual and required capital ratios as of December 31, 2019 and December 31, 2018 for Cullen/Frost and Frost Bank under the Basel III Capital Rules. The minimum required capital amounts presented include the minimum required capital levels as of December 31, 2019 and December 31, 2018 based on the phase-in provisions of the Basel III Capital Rules and the minimum required capital levels as of January 1, 2019 when the Basel III Capital Rules have been fully phased-in. Capital levels required to be considered well capitalized are based upon prompt corrective action regulations, as amended to reflect the changes under the Basel III Capital Rules.

	Actual				Minimum Capital Required - Basel III Fully Phased-In				Required to be Considered Well Capitalized
	Capital Amount		Ratio		Capital Amount		Ratio		Capital Amount		Ratio
2019
Common Equity Tier 1 to Risk-Weighted Assets
Cullen/Frost	$	2,857,250	12.36	%	$	1,617,886	7.00	%	$	1,502,323	6.50	%
Frost Bank	2,958,326		12.82		1,615,206		7.00		1,499,834		6.50
Tier 1 Capital to Risk-Weighted Assets
Cullen/Frost	3,001,736		12.99		1,964,576		8.50		1,849,013		8.00
Frost Bank	2,958,326		12.82		1,961,322		8.50		1,845,950		8.00
Total Capital to Risk-Weighted Assets
Cullen/Frost	3,367,403		14.57		2,426,829		10.50		2,311,266		10.00
Frost Bank	3,090,993		13.40		2,422,809		10.50		2,307,438		10.00
Leverage Ratio
Cullen/Frost	3,001,736		9.28		1,293,188		4.00		1,616,485		5.00
Frost Bank	2,958,326		9.15		1,292,743		4.00		1,615,929		5.00

	Actual				Minimum Capital Required - Basel III Phase-In Schedule				Minimum Capital Required - Basel III Fully Phased-In				Required to be Considered Well Capitalized
	Capital Amount		Ratio		Capital Amount		Ratio		Capital Amount		Ratio		Capital Amount		Ratio
2018
Common Equity Tier 1 to Risk-Weighted Assets
Cullen/Frost	$	2,642,475	12.27	%	$	1,372,573	6.375	%	$	1,507,139	7.00	%	$	1,399,486	6.50	%
Frost Bank	2,743,973		12.78		1,368,701		6.375		1,502,887		7.00		1,395,538		6.50
Tier 1 Capital to Risk-Weighted Assets
Cullen/Frost	2,786,961		12.94		1,695,532		7.875		1,830,098		8.50		1,722,445		8.00
Frost Bank	2,743,973		12.78		1,690,748		7.875		1,824,934		8.50		1,717,585		8.00
Total Capital to Risk-Weighted Assets
Cullen/Frost	3,152,593		14.64		2,126,143		9.875		2,260,709		10.50		2,153,056		10.00
Frost Bank	2,876,605		13.40		2,120,144		9.875		2,254,331		10.50		2,146,982		10.00
Leverage Ratio
Cullen/Frost	2,786,961		9.06		1,231,028		4.00		1,231,028		4.00		1,538,785		5.00
Frost Bank	2,743,973		8.93		1,229,650		4.00		1,229,650		4.00		1,537,062		5.00