Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jun. 30, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent	$ 2,745		$ 2,745		$ 2,489
Regulatory liabilities	69		69		87
Revenue	1,575	$ 1,546	4,882	$ 5,050
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent	2,745		2,745		2,489
Regulatory liabilities	69		69		87
Revenue	1,450	$ 1,429	4,524	$ 4,706
Gain Shared with Customers for Substation Transmission Assets to METC | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities					17
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Requested recovery collection						$ 34
Revenue					$ 34
COVID-19 Costs Accounting Deferral | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent	$ 5		$ 5