Contingencies and Commitments (Guarantees) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Jul. 31, 2020
Variable Interest Entity, Primary Beneficiary | Aviator Wind Class B Membership
Guarantees And Other Contingencies [Line Items]
Ownership percentage		49.00%
Guarantees
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 30
Carrying Amount	$ 0
Guarantees | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 30
Carrying Amount	$ 0
Indemnification Agreement From Purchase Of Variable Interest Entity
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 341
Carrying Amount	$ 0
Indemnity Obligations From Stock And Asset Sales Agreements
Guarantees And Other Contingencies [Line Items]
Expiration Date	indefinite
Maximum Obligation	$ 153
Carrying Amount	2
Tax And Other Indemnity Obligations | Consumers Energy Company
Guarantees And Other Contingencies [Line Items]
Carrying Amount	$ 1