Regulatory Matters - Quarterly Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 204		$ 151
Operating Revenue	2,083	$ 1,864
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	204		151
Operating Revenue	1,937	$ 1,744
Consumers Energy Company | Energy Waste Reduction Plan Incentive
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection	42
Operating Revenue			42
Reserve for customer refunds | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	28		28
Gain shared with customers | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities	$ 14		$ 14