Retirement Benefits (Schedule of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	$ 1,468	$ 1,208
Non-current liabilities	106	108
Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	1,367	1,126
Non-current liabilities	77	79
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	809	651
DB Pension Plans | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	781	632
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	659	557
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Non-current assets	586	494
DB SERP
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	10	10
Non-current liabilities	104	107
DB SERP | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	7	7
Non-current liabilities	$ 76	$ 78