Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Debt Instrument [Line Items]
Medium- and long-term debt	$ 5,422	$ 6,673
Parent company
Debt Instrument [Line Items]
Medium- and long-term notes	1,543	1,503
Medium- and long-term debt	1,790	1,746
Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	626	953
Long-Term Federal Home Loan Bank Advances	3,006	3,974
Medium- and long-term debt	3,632	4,927
3.80% subordinated notes due 2026 \| Parent company
Debt Instrument [Line Items]
Subordinated notes	$ 247	243
Stated interest rate	3.80%
Maturity year	2026
4.00% notes due 2029 \| Parent company
Debt Instrument [Line Items]
Medium- and long-term notes	$ 535	519
Stated interest rate	4.00%
Maturity year	2029
5.982% Notes Due 2030 \| Parent company
Debt Instrument [Line Items]
Medium- and long-term notes	$ 1,008	984
Stated interest rate	5.982%
Maturity year	2030
4.00% subordinated notes due 2025 \| Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	$ 0	345
Stated interest rate	4.00%
Maturity year	2025
7.875% subordinated notes due 2026 \| Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	$ 154	157
Stated interest rate	7.875%
Maturity year	2026
5.332 subordinated notes due 2033 \| Subsidiaries
Debt Instrument [Line Items]
Subordinated notes	$ 472	451
Stated interest rate	5.332%
Maturity year	2033
5.07% advance due 2025 \| Subsidiaries
Debt Instrument [Line Items]
Long-Term Federal Home Loan Bank Advances	$ 0	1,000
Stated interest rate	5.07%
Maturity year	2025
4.79% advance due 2026 \| Subsidiaries
Debt Instrument [Line Items]
Long-Term Federal Home Loan Bank Advances	$ 1,000	997
Stated interest rate	4.79%
Maturity year	2026
4.49% advance due 2027 \| Subsidiaries
Debt Instrument [Line Items]
Long-Term Federal Home Loan Bank Advances	$ 1,003	992
Stated interest rate	4.49%
Maturity year	2027
4.49% advance due 2028 \| Subsidiaries
Debt Instrument [Line Items]
Long-Term Federal Home Loan Bank Advances	$ 1,003	$ 985
Stated interest rate	4.49%
Maturity year	2028

COMERICA INC 10-Q