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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%