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Revenue (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
Dec. 31, 2022
Disaggregation of Revenue [Line Items]          
Unbilled receivables $ 321   $ 321   $ 663
Incentive revenue collection period 24 months   24 months    
Consumers Energy Company          
Disaggregation of Revenue [Line Items]          
Unbilled receivables $ 321   $ 321   $ 663
Accounts Receivable          
Disaggregation of Revenue [Line Items]          
Bad debt expense 15 $ 13 32 $ 31  
Accounts Receivable | Consumers Energy Company          
Disaggregation of Revenue [Line Items]          
Bad debt expense $ 15 $ 13 $ 32 $ 31