Retirement Benefits (Schedule of SERP Trust Assets, ABO and Contributions) (Details) - DB SERP - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
ABO	$ 105	$ 115
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
ABO	76	83
Trust assets
Defined Benefit Plan Disclosure [Line Items]
Trust assets	127	132
Trust assets | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Trust assets	$ 95	$ 98