Retirement Benefits (Schedule of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	$ 1,627	$ 1,468
Non-current liabilities	96	106
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	1,514	1,367
Non-current liabilities	70	77
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	870	809
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	836	781
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	757	659
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	678	586
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	10
Non-current liabilities	95	104
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	$ 69	$ 76