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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%