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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%

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- Definition Amount of total capital as defined by regulatory framework. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI https://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826 + Details
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