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Retirement Benefits (Narrative) (Details) $ in Millions |  | 2 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2021 USD ($) year | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Union employees percentage |  | 41.00% | 41.00% |  |
Consumers Energy Company |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Union employees percentage |  | 42.00% | 42.00% |  |
DB Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Settlement loss | $ 18 | $ 4 |  |  |
Amortized net gains and losses in excess of PBO or MRV |  |  | 10.00% |  |
Period for gains or losses to be included in market related value |  |  | 5 years |  |
ABO |  | 2,700 | $ 2,700 | $ 2,900 |
DB Pension Plans | Consumers Energy Company | Pension Costs |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Settlement loss | $ 18 | $ 3 |  |  |
DB Pension Plans | Equity securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 54.00% | 54.00% |  |
DB Pension Plans | Fixed-income securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 29.00% | 29.00% |  |
DB Pension Plans | Real asset investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 12.00% | 12.00% |  |
DB Pension Plans | Multi-asset investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 5.00% | 5.00% |  |
OPEB Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Settlement loss |  |  | $ 0 | $ 0 | $ 0
Retirement age requirement | year |  |  | 55 |  |
Retirement years of service |  |  | 10 years |  |
Retirement years of service with disability |  |  | 15 years |  |
Ultimate health care cost trend rate |  | 4.75% | 4.75% |  |
Year health care cost trend rate reaches ultimate trend rate |  |  | 2028 |  |
Estimated time of amortization of gains losses |  |  | 9 years | 9 years | 10 years
OPEB Plan | Under Age 65 |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Health care cost trend rate assumed next fiscal year |  | 6.25% | 6.25% | 6.50% |
OPEB Plan | Over Age 65 |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Health care cost trend rate assumed next fiscal year |  | 6.75% | 6.75% | 7.00% |
OPEB Plan | Consumers Energy Company |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Retirement age requirement | year |  |  | 55 |  |
Retirement years of service |  |  | 10 years |  |
Retirement years of service with disability |  |  | 15 years |  |
Ultimate health care cost trend rate |  | 4.75% | 4.75% |  |
Year health care cost trend rate reaches ultimate trend rate |  |  | 2028 |  |
OPEB Plan | Consumers Energy Company | Under Age 65 |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Health care cost trend rate assumed next fiscal year |  | 6.25% | 6.25% | 6.50% |
OPEB Plan | Consumers Energy Company | Over Age 65 |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Health care cost trend rate assumed next fiscal year |  | 6.75% | 6.75% | 7.00% |
Postretirement Health Trusts | Equity securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 55.00% | 55.00% |  |
Postretirement Health Trusts | Fixed-income securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 30.00% | 30.00% |  |
Postretirement Health Trusts | Real asset investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 12.00% | 12.00% |  |
Postretirement Health Trusts | Multi-asset investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 3.00% | 3.00% |  |
Postretirement Life Trusts | Equity securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 53.00% | 53.00% |  |
Postretirement Life Trusts | Fixed-income securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 32.00% | 32.00% |  |
Postretirement Life Trusts | Multi-asset investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target allocation percentage |  | 15.00% | 15.00% |  |
DB Pension Plan A Settlement | DB Pension Plans | Pension Costs |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Regulatory asset, amortization period |  |  | 8 years |  |
Defined Company Contribution Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan |  |  | $ 41 | $ 31 | $ 29
Defined Company Contribution Plan | Consumers Energy Company |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan |  |  | 41 | 31 | 28
DC SERP |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan |  |  | $ 2 | 2 | 2
Minimum years of participation before vesting |  |  | 5 years |  |
Trust assets |  | $ 13 | $ 13 | 11 |
401 (K) Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer match of eligible wages |  |  | 3.00% |  |
Plan cost, defined contribution plan |  |  | $ 31 | 29 | 28
Employer match of eligible contributions |  |  | 100.00% |  |
Secondary employer match of eligible contributions |  |  | 50.00% |  |
Secondary employer match of eligible wages |  |  | 2.00% |  |
401 (K) Plan | Consumers Energy Company |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan cost, defined contribution plan |  |  | $ 31 | $ 29 | $ 27
Pension Plan A | DB Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated time of amortization of gains losses |  |  | 8 years | 8 years | 9 years
Estimated time of prior service cost |  |  | 8 years |  |
Pension Plan A | DB Pension Plans | Consumers Energy Company |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated time of prior service cost |  |  | 8 years |  |
Pension Plan B | DB Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Estimated time of amortization of gains (losses) life expectancy |  |  | 18 years | 19 years | 20 years
Minimum | Defined Company Contribution Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer match of eligible wages |  |  | 5.00% |  |
Minimum | DC SERP |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan contribution percentage |  |  | 5.00% |  |
Maximum | Defined Company Contribution Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Employer match of eligible wages |  |  | 10.00% |  |
Maximum | DC SERP |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan contribution percentage |  |  | 15.00% |  |

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