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Retirement Benefits (Schedule of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets $ 1,468 $ 1,208
Non-current liabilities 106 108
Consumers Energy Company    
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets 1,367 1,126
Non-current liabilities 77 79
DB Pension Plans    
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets 809 651
DB Pension Plans | Consumers Energy Company    
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets 781 632
OPEB Plan    
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets 659 557
OPEB Plan | Consumers Energy Company    
Defined Benefit Plan Disclosure [Line Items]    
Non-current assets 586 494
DB SERP    
Defined Benefit Plan Disclosure [Line Items]    
Current liabilities 10 10
Non-current liabilities 104 107
DB SERP | Consumers Energy Company    
Defined Benefit Plan Disclosure [Line Items]    
Current liabilities 7 7
Non-current liabilities $ 76 $ 78