Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	May 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current	$ 88		$ 87
Revenue	1,864	$ 2,059
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current	88		87
Revenue	1,744	$ 1,943
Gain Shared with Customers for Substation Transmission Assets to METC | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current	$ 17		17
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Revenue			$ 34
Forecast | Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery collection				$ 34