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Long-Term Debt (Details) - USD ($)
Jun. 10, 2026
Jan. 29, 2026
Feb. 01, 2026
Comerica Incorporated      
Debt Instrument [Line Items]      
Long-term debt assumed     $ 5,529,000,000
Long-term debt assumed     $ 5,529,000,000
Senior Notes | Fixed Rate Floating Rate 4.566% Senior Notes Due 2032 | Parent Company      
Debt Instrument [Line Items]      
Principal amount   $ 1,000,000,000.0  
Senior Notes | Fixed-Rate/Floating-Rate 4.566 Percent Senior Notes Due April 29, 2032 | Parent Company      
Debt Instrument [Line Items]      
Interest rate   4.566%  
Basis spread on variable rate (as a percent)   0.95%  
Senior Notes | Fixed-Rate/Floating-Rate 4.566 Percent Senior Notes Due April 29, 2032 | Redemption Period One | Parent Company      
Debt Instrument [Line Items]      
Redemption period   180 days  
Senior Notes | Fixed-Rate/Floating-Rate 4.566 Percent Senior Notes Due April 29, 2032 | Redemption Period Two | Parent Company      
Debt Instrument [Line Items]      
Redemption period   30 days  
Senior Notes | Fixed-Rate/Floating-Rate 5.141 Percent Senior Notes Due January 29, 2037 | Parent Company      
Debt Instrument [Line Items]      
Principal amount   $ 1,000,000,000.0  
Interest rate   5.141%  
Basis spread on variable rate (as a percent)   1.24%  
Senior Notes | Fixed-Rate/Floating-Rate 5.141 Percent Senior Notes Due January 29, 2037 | Redemption Period One | Parent Company      
Debt Instrument [Line Items]      
Redemption period   180 days  
Senior Notes | Fixed-Rate/Floating-Rate 5.141 Percent Senior Notes Due January 29, 2037 | Redemption Period Two | Parent Company      
Debt Instrument [Line Items]      
Redemption period   90 days  
Senior Notes | Fixed-Rate 4.00% Senior Notes Due in 2029      
Debt Instrument [Line Items]      
Principal amount $ 335,000,000    
Interest rate 4.00%    
Senior Notes | Fixed-Rate 4.00% Senior Notes Due in 2029 | Comerica Incorporated      
Debt Instrument [Line Items]      
Principal amount $ 550,000,000    
Interest rate 4.00%   4.00%
Long-term debt assumed     $ 547,000,000
Senior Notes | Fixed-Rate 5.982% Senior Notes Due 2030      
Debt Instrument [Line Items]      
Principal amount $ 938,000,000    
Interest rate 5.982%    
Senior Notes | Fixed-Rate 5.982% Senior Notes Due 2030 | SOFR      
Debt Instrument [Line Items]      
Basis spread on variable rate (as a percent) 2.155%    
Senior Notes | Fixed-Rate 5.982% Senior Notes Due 2030 | Treasury Rate      
Debt Instrument [Line Items]      
Basis spread on variable rate (as a percent) 0.30%    
Senior Notes | Fixed-Rate 5.982% Senior Notes Due 2030 | Comerica Incorporated      
Debt Instrument [Line Items]      
Principal amount $ 1,000,000,000.0    
Interest rate 5.982%   5.982%
Long-term debt assumed     $ 1,046,000,000