Asset Sales and Exit Activities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended		15 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory liabilities	$ 151	$ 87	$ 151
Electric Utility | Gain shared with customers | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposition of assets	14
Consumers Energy Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory liabilities	151	87	151
Retention Benefits | D.E. Karn Generating Complex
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected cost	35		35
Retention and severance costs	13	3	16
Costs incurred and capitalized	2	1
Retention Benefits | D.E. Karn Generating Complex | Property, Plant and Equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs incurred and capitalized			3
Gain shared with customers | Consumers Energy Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Regulatory liabilities	$ 14	$ 17	$ 14