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Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | $ 436 | $ 766
Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 392 | 711
DB Pension Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 38 | 143
Non-current liabilities | 303 | 618
DB Pension Plans | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 49 | 147
Non-current liabilities | 295 | 602
DB SERP |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 10 | 9
Non-current liabilities | 130 | 145
DB SERP | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 7 | 7
Non-current liabilities | 94 | 105
OPEB Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | 235 | 323
OPEB Plan | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current assets | $ 193 | $ 276

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