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Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | $ 674 | $ 436
Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 622 | 392
DB Pension Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 104 | 38
Non-current liabilities | 531 | 303
DB Pension Plans | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 109 | 49
Non-current liabilities | 517 | 295
OPEB Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 344 | 235
OPEB Plan | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 290 | 193
DB SERP |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 10 | 10
Non-current liabilities | 140 | 130
DB SERP | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 7 | 7
Non-current liabilities | $ 102 | $ 94

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