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Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Summary of Capital Position) (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Summary of Capital Position [Line Items] |  |  |
Tier 1 capital | $ 4,400 | $ 4,600 |
Total capital | 5,800 |  | $ 6,100
Minimum |  |  |
Summary of Capital Position [Line Items] |  |  |
CET 1 capital | $ 3,300 | $ 3,400 |
CET 1 capital to risk-weighted assets | 4.50% | 4.50% |
Banking Regulation, Tier 1 Risk-Based Capital Ratio, Capital Adequacy, Minimum | 0.060 | 0.060 |
Total capital to risk-weighted assets | 0.080 | 0.080 |
Tier 1 capital to average assets | 0.040 | 0.040 |
Banking Regulation, Capital Conservation Buffer, Total Risk-Based Capital, Actual |  | 0.025 |
Capital conservation buffer | 0.025 |  |
Comerica Incorporated |  |  |
Summary of Capital Position [Line Items] |  |  |
CET 1 capital | $ 8,667 | $ 8,414 |
Tier 1 capital | 9,061 | 8,808 |
Total capital | 10,363 | 10,263 |
Risk-weighted assets | 72,903 | 75,901 |
Average assets (fourth quarter) | $ 81,797 | $ 87,538 |
CET 1 capital to risk-weighted assets | 11.89% | 11.09% |
Banking Regulation, Tier 1 Risk-Based Capital Ratio, Actual | 0.1243 | 0.1160 |
Total capital to risk-weighted assets | 0.1421 | 0.1352 |
Tier 1 capital to average assets | 0.1108 | 0.1006 |
Capital conservation buffer | 0.0621 | 0.0552 |
Comerica Bank |  |  |
Summary of Capital Position [Line Items] |  |  |
CET 1 capital | $ 8,547 | $ 8,007 |
Tier 1 capital | 8,547 | 8,007 |
Total capital | 9,799 | 9,362 |
Risk-weighted assets | 72,833 | 75,783 |
Average assets (fourth quarter) | $ 81,643 | $ 87,423 |
CET 1 capital to risk-weighted assets | 11.74% | 10.57% |
Banking Regulation, Tier 1 Risk-Based Capital Ratio, Actual | 0.1174 | 0.1057 |
Total capital to risk-weighted assets | 0.1345 | 0.1235 |
Tier 1 capital to average assets | 0.1047 | 0.0916 |
Capital conservation buffer | 0.0545 | 0.0435 |

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- Definition Capital conservation buffer percentage calculated as Tier 1 risk-based capital ratio after deduction of minimum Tier 1 risk-based capital ratio as defined by regulatory framework. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477270/942-505-50-1 + Details
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