Fair Value Measurements (Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets
Restricted cash equivalents	$ 70	$ 75
Consumers Energy Company
Assets
Restricted cash equivalents	69	75
Fair Value, Inputs, Level 1, 2 and 3
Assets
Total assets	183	138
Liabilities
Total liabilities	39	34
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total assets	99	102
Liabilities
Total liabilities	27	25
Fair Value, Inputs, Level 1
Assets
Cash equivalents	75	27
Restricted cash equivalents	70	75
Nonqualified deferred compensation plan assets	35	34
Liabilities
Nonqualified deferred compensation plan liabilities	35	34
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Cash equivalents	0	0
Restricted cash equivalents	69	75
Nonqualified deferred compensation plan assets	27	25
Liabilities
Nonqualified deferred compensation plan liabilities	27	25
Fair Value, Inputs, Level 2 And Level 3
Assets
Derivative instruments	3	2
Liabilities
Derivative instruments	4	0
Fair Value, Inputs, Level 2 And Level 3 | Consumers Energy Company
Assets
Derivative instruments	3	2
Liabilities
Derivative instruments	$ 0	$ 0