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Retirement Benefits (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 USD ($) yr | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |
Union employees percentage | 44.00% |  |
OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Retirement age requirement | yr | 55 |  |
Retirement years of service | 10 years |  |
Retirement years of service with disability | 15 years |  |
Ultimate health care cost trend rate | 4.75% |  |
Year health care cost trend rate reaches ultimate trend rate | 2032 |  |
Estimated time of amortization of gains losses | 9 years | 9 years | 9 years
OPEB Plan | Volatility Mechanism |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Deferred costs (credits) | $ (23) |  |
OPEB Plan | Under Age 65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate assumed next fiscal year | 8.00% | 6.50% |
OPEB Plan | Over Age 65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate assumed next fiscal year | 8.50% | 6.75% |
DB Pension Plans and DB SERP | Volatility Mechanism |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Deferred costs (credits) | $ 11 |  |
DB Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
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 |  |
Accumulated benefit obligation | $ 2,000 | $ 2,000 |
DB Pension Plans | Fixed-income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 40.00% |  |
DB Pension Plans | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 38.00% |  |
DB Pension Plans | Real asset investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 11.00% |  |
DB Pension Plans | Return-seeking fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 7.00% |  |
DB Pension Plans | Liquid alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 4.00% |  |
Postretirement Health Trusts | Fixed-income securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 40.00% |  |
Postretirement Health Trusts | Equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 38.00% |  |
Postretirement Health Trusts | Real asset investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 11.00% |  |
Postretirement Health Trusts | Return-seeking fixed income |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 7.00% |  |
Postretirement Health Trusts | Liquid alternative investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Target allocation percentage | 4.00% |  |
Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Union employees percentage | 45.00% |  |
Consumers Energy Company | OPEB Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Retirement age requirement | yr | 55 |  |
Retirement years of service | 10 years |  |
Retirement years of service with disability | 15 years |  |
Ultimate health care cost trend rate | 4.75% |  |
Year health care cost trend rate reaches ultimate trend rate | 2032 |  |
Consumers Energy Company | OPEB Plan | Under Age 65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate assumed next fiscal year | 8.00% | 6.50% |
Consumers Energy Company | OPEB Plan | Over Age 65 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Health care cost trend rate assumed next fiscal year | 8.50% | 6.75% |
Defined Company Contribution Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan cost, defined contribution plan | $ 51 | $ 48 | $ 41
Defined Company Contribution Plan | Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan cost, defined contribution plan | 50 | 48 | 41
DC SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan cost, defined contribution plan | $ 1 | 1 | 2
Minimum years of participation before vesting | 5 years |  |
Defined Contribution Plan, Trust Assets, Amount | $ 14 | 12 |
401 (K) Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan cost, defined contribution plan | 41 | 44 | 31
401 (K) Plan | Consumers Energy Company |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan cost, defined contribution plan | $ 40 | $ 43 | $ 31
Pension Plan A | DB Pension Plans |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Estimated time of amortization of gains losses | 8 years | 8 years | 8 years
Estimated time of prior service cost |  |  | 8 years
Pension Plan A | Consumers Energy Company | DB Pension Plans |  |  |
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 | 17 years | 18 years | 18 years
Minimum | Defined Company Contribution Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contribution range | 5.00% |  |
Minimum | DC SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan contribution percentage | 5.00% |  |
Minimum | 401 (K) Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contribution range | 4.00% |  |
Maximum | Defined Company Contribution Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contribution range | 10.00% |  |
Maximum | DC SERP |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan contribution percentage | 15.00% |  |
Maximum | 401 (K) Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contribution range | 6.00% |  |

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