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Retirement Benefits (Schedule of SERP Trust Assets, ABO and Contributions) (Details) - DB SERP - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
ABO | $ 115 | $ 118
Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
ABO | 83 | 85
Trust assets |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Trust assets | 132 | 137
Trust assets | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Trust assets | $ 98 | $ 101

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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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