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Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Summary of Capital Position) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Minimum    
Summary of Capital Position [Line Items]    
CET 1 capital $ 3,500 $ 3,100
Tier 1 capital 4,700 4,200
Total capital $ 6,300 $ 5,600
CET 1 capital to risk-weighted assets 4.50% 4.50%
Tier 1 capital to risk-weighted assets 6.00% 6.00%
Total capital to risk-weighted assets 8.00% 8.00%
Tier 1 capital to average assets 4.00% 4.00%
Capital conservation buffer 2.50% 2.50%
Comerica Incorporated    
Summary of Capital Position [Line Items]    
CET 1 capital $ 7,884 $ 7,064
Tier 1 capital 8,278 7,458
Total capital 9,817 8,608
Risk-weighted assets 78,871 69,708
Average assets (fourth quarter) $ 86,726 $ 96,417
CET 1 capital to risk-weighted assets 10.00% 10.13%
Tier 1 capital to risk-weighted assets 10.50% 10.70%
Total capital to risk-weighted assets 12.45% 12.35%
Tier 1 capital to average assets 9.55% 7.74%
Capital conservation buffer 4.45% 4.35%
Comerica Bank    
Summary of Capital Position [Line Items]    
CET 1 capital $ 7,801 $ 7,634
Tier 1 capital 7,801 7,634
Total capital 9,190 8,584
Risk-weighted assets 78,781 69,542
Average assets (fourth quarter) $ 86,608 $ 96,216
CET 1 capital to risk-weighted assets 9.90% 10.98%
Tier 1 capital to risk-weighted assets 9.90% 10.98%
Total capital to risk-weighted assets 11.67% 12.34%
Tier 1 capital to average assets 9.01% 7.93%
Capital conservation buffer 3.67% 4.34%