Retirement Benefits (Schedule of SERP Trust Assets, ABO and Contributions) (Details) - DB SERP - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Defined Benefit Plan Disclosure [Line Items]
ABO	$ 104	$ 105
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
ABO	76	76
Trust assets
Defined Benefit Plan Disclosure [Line Items]
Trust assets	122	127
Trust assets | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Trust assets	$ 92	$ 95