Regulatory Matters - Quarterly Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 191		$ 191		$ 151
Operating Revenue	1,725	$ 1,507	5,296	$ 4,691
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	191		191		151
Operating Revenue	1,644	$ 1,450	5,074	$ 4,524
Consumers Energy Company | Reserve for customer refunds
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	8		8		28
Consumers Energy Company | Gain shared with customers
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities					14
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