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Retirement Benefits (Schedule of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Consumers Energy Company    
Regulatory assets    
Total regulatory assets $ 3,886 $ 3,652
DB Pension Plans and DB SERP    
Regulatory assets    
Net loss 634 724
Prior service cost (credit) 16 21
Total regulatory assets 650 745
AOCI    
Net loss (gain) 65 69
Prior service cost (credit) 1 1
Total amounts recognized in regulatory assets and AOCI 716 815
DB Pension Plans and DB SERP | Consumers Energy Company    
Regulatory assets    
Net loss 634 724
Prior service cost (credit) 16 21
Total regulatory assets 650 745
AOCI    
Net loss (gain) 20 20
Total amounts recognized in regulatory assets and AOCI 670 765
OPEB Plan    
Regulatory assets    
Net loss 191 251
Prior service cost (credit) (100) (140)
Total regulatory assets 91 111
AOCI    
Net loss (gain) (3) 2
Prior service cost (credit) (2) (3)
Total amounts recognized in regulatory assets and AOCI 86 110
OPEB Plan | Consumers Energy Company    
Regulatory assets    
Net loss 191 251
Prior service cost (credit) (100) (140)
Total regulatory assets 91 111
AOCI    
Net loss (gain) 0 0
Total amounts recognized in regulatory assets and AOCI $ 91 $ 111