Fair Value Measurements (Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Assets
Restricted cash equivalents	$ 61	$ 75
Consumers Energy Company
Assets
Restricted cash equivalents	60	75
Fair Value, Inputs, Level 1, 2 and 3
Assets
Total assets	364	138
Liabilities
Total liabilities	36	34
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total assets	85	102
Liabilities
Total liabilities	24	25
Fair Value, Inputs, Level 1
Assets
Cash equivalents	269	27
Restricted cash equivalents	61	75
Nonqualified deferred compensation plan assets	33	34
Liabilities
Nonqualified deferred compensation plan liabilities	33	34
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Cash equivalents	0	0
Restricted cash equivalents	60	75
Nonqualified deferred compensation plan assets	24	25
Liabilities
Nonqualified deferred compensation plan liabilities	24	25
Fair Value, Inputs, Level 2 And Level 3
Assets
Derivative instruments	1	2
Liabilities
Derivative instruments	3	0
Fair Value, Inputs, Level 2 And Level 3 | Consumers Energy Company
Assets
Derivative instruments	1	2
Liabilities
Derivative instruments	$ 0	$ 0