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Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 712 | $ 10 | $ 252
Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 690 | 7 | $ 242
DB Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 700 | 0 |
DB Pension Plans | Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 682 | 0 |
OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 1 | 0 |
OPEB Plan | Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 1 | $ 0 |

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- Definition Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585 + Details
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