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Retirement Benefits (Quarterly Narrative) (Details) - DB Pension Plans - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Mar. 31, 2022 | Mar. 31, 2022
Defined Benefit Plan Disclosure [Line Items] |  |
Settlement loss | $ 4 |
Increase (decrease) in non-current pension plan assets |  | $ 91
Loss to AOCI |  | 2
Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Increase (decrease) in non-current pension plan assets |  | $ 89
Pension Costs |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Settlement loss | 4 |
Increase (decrease) in non-current pension plan assets | (89) |
Pension Costs | DB Pension Plan A Settlement |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory asset collection period |  | 8 years
Pension Costs | Consumers Energy Company |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Settlement loss | 4 |
Increase (decrease) in non-current pension plan assets | $ (89) |

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