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Financings and Capitalization (First Mortgage Bond Purchase) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Debt Instrument [Line Items]      
Principal (In Millions) $ 3,556    
Unamortized discounts (30) $ (30)  
Unamortized issuance costs (135) (120)  
Long-term debt 14,508 13,122  
Gain on debt extinguishment   0 $ 0
Interest on long-term debt 616 509 481
Consumers Energy Company      
Debt Instrument [Line Items]      
Principal (In Millions) 2,671    
Unamortized discounts (28) (27)  
Unamortized issuance costs (73) (67)  
Long-term debt 10,037 9,192  
Interest on long-term debt 415 325 294
Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) 431    
Long-term debt 424 0  
CMS Energy      
Debt Instrument [Line Items]      
Principal (In Millions) 800    
Long-term debt 4,471 3,930  
Interest on long-term debt 201 $ 181 $ 183
First mortgage bonds      
Debt Instrument [Line Items]      
Gain on debt extinguishment 131    
First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) 431    
Unamortized discounts (3)    
Unamortized issuance costs (4)    
Long-term debt 424    
First mortgage bonds | CMS Energy      
Debt Instrument [Line Items]      
Payment for purchase of first mortgage bonds $ 293    
First mortgage bonds due 2060 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 2.50%    
First mortgage bonds due 2060 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 163    
First mortgage bonds due 2052 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 2.65%    
First mortgage bonds due 2052 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 106    
First mortgage bonds due 2050 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 3.75%    
First mortgage bonds due 2050 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 23    
First mortgage bonds due 2050 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 3.10%    
First mortgage bonds due 2050 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 52    
First mortgage bonds due 2051 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 3.50%    
First mortgage bonds due 2051 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 27    
First mortgage bonds due 2048 | First mortgage bonds | Consumers Energy Company      
Debt Instrument [Line Items]      
Interest rate 4.05%    
First mortgage bonds due 2048 | First mortgage bonds | Consumers Energy Company | Related Party      
Debt Instrument [Line Items]      
Principal (In Millions) $ 60    
Repurchased Debt | First mortgage bonds      
Debt Instrument [Line Items]      
Interest on long-term debt $ 5