Regulatory Matters - Quarterly Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 214		$ 214		$ 151
Operating Revenue	1,558	$ 1,382	3,571	$ 3,184
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	214		214		151
Operating Revenue	1,493	$ 1,330	3,430	$ 3,074
Consumers Energy Company | Electric Rate Case
Public Utilities, General Disclosures [Line Items]
Recommended disallowed costs	39		39
Consumers Energy Company | Energy Waste Reduction Plan Incentive
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection	42		42
Operating Revenue					42
Reserve for customer refunds | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	23		23		28
Gain shared with customers | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 14		$ 14		$ 14