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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, 2023 | Dec. 31, 2022
Summary of Capital Position [Line Items] |  |
Tier 1 capital | $ 4,600 | $ 4,700
Total capital | 6,100 | 6,300
Minimum |  |
Summary of Capital Position [Line Items] |  |
CET 1 capital | $ 3,400 | $ 3,500
CET 1 capital to risk-weighted assets | 4.50% | 4.50%
Tier 1 capital to risk-weighted assets - 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
Capital conservation buffer | 0.025 | 0.025
Comerica Incorporated |  |
Summary of Capital Position [Line Items] |  |
CET 1 capital | $ 8,414 | $ 7,884
Tier 1 capital | 8,808 | 8,278
Total capital | 10,263 | 9,817
Risk-weighted assets | 75,901 | 78,871
Average assets (fourth quarter) | $ 87,538 | $ 86,726
CET 1 capital to risk-weighted assets | 11.09% | 10.00%
Total capital to risk-weighted assets | 0.1352 | 0.1245
Tier 1 capital to average assets | 0.1006 | 0.0955
Capital conservation buffer | 0.0552 | 0.0445
Tier 1 capital to risk-weighted assets | 0.1160 | 0.1050
Comerica Bank |  |
Summary of Capital Position [Line Items] |  |
CET 1 capital | $ 8,007 | $ 7,801
Tier 1 capital | 8,007 | 7,801
Total capital | 9,362 | 9,190
Risk-weighted assets | 75,783 | 78,781
Average assets (fourth quarter) | $ 87,423 | $ 86,608
CET 1 capital to risk-weighted assets | 10.57% | 9.90%
Total capital to risk-weighted assets | 0.1235 | 0.1167
Tier 1 capital to average assets | 0.0916 | 0.0901
Capital conservation buffer | 0.0435 | 0.0367
Tier 1 capital to risk-weighted assets | 0.1057 | 0.0990

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- Definition Common Equity Tier One Risk Based Capital To Risk Weighted Assets as defined by regulations. + References No definition available. + Details
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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//1943274/2147480696/942-505-50-1 + Details
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- Definition Ratio of minimum total risk-based capital to risk-weighted assets required for capital adequacy 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//1943274/2147480696/942-505-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 505 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Publisher FASB -URI https://asc.fasb.org//1943274/2147480696/942-505-50-1B + Details
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