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Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | $ 142 | $ 152
Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 104 | 112
DB Pension Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 529 | 136
DB Pension Plans | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 510 | 138
OPEB Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 621 | 440
OPEB Plan | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 546 | 377
DB SERP |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 10 | 10
Non-current liabilities | 139 | 150
DB SERP | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 7 | 7
Non-current liabilities | $ 102 | $ 110

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