Asset Sales and Exit Activities - Narrative (Details) $ in Millions	1 Months Ended		3 Months Ended
	Sep. 30, 2019 USD ($) coal_fueled_electric_generating_unit	Apr. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Oct. 24, 2019 USD ($)
DIG's High-Voltage Equipment to ITC | 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		$ 16
Electric Utility | Substation Transmission Assets to METC | 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	$ 34
Consumers Energy Company | Coal-Fueled Electric Generating Units to be Retired
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of units | coal_fueled_electric_generating_unit	2
D.E. Karn Generating Complex | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected cost				$ 35
Retention and Severance Benefits | D.E. Karn Generating Complex | Forecast | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Retention and severance costs			$ 6