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Regulatory Matters (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]          
Regulatory assets, noncurrent $ 2,485   $ 2,485   $ 2,489
Regulatory liabilities 84   84   87
Revenue 1,443 $ 1,445 3,307 $ 3,504  
Consumers Energy Company          
Public Utilities, General Disclosures [Line Items]          
Regulatory assets, noncurrent 2,485   2,485   2,489
Regulatory liabilities 84   84   87
Revenue 1,330 $ 1,334 3,074 $ 3,277  
Gain Shared with Customers for Substation Transmission Assets to METC | Consumers Energy Company          
Public Utilities, General Disclosures [Line Items]          
Regulatory liabilities 15   15   17
Energy Waste Reduction Plan Incentive | Consumers Energy Company          
Public Utilities, General Disclosures [Line Items]          
Requested recovery collection 34   34    
Revenue         $ 34
COVID-19 Costs Accounting Deferral | Consumers Energy Company          
Public Utilities, General Disclosures [Line Items]          
Regulatory assets, noncurrent $ 9   $ 9