Fair Value Measurements (Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets
Restricted cash equivalents	$ 59	$ 21
Derivative instruments	1	2
Consumers Energy Company
Assets
Restricted cash equivalents	59	21
Derivative instruments	1	2
Fair Value, Inputs, Level 1
Assets
Cash equivalents	264	18
Restricted cash equivalents	59	21
Nonqualified deferred compensation plan assets	31	30
Liabilities
Nonqualified deferred compensation plan liabilities	31	30
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Cash equivalents	198	0
Restricted cash equivalents	59	21
Nonqualified deferred compensation plan assets	23	22
Liabilities
Nonqualified deferred compensation plan liabilities	23	22
Fair Value, Inputs, Level 1, 2 and 3
Assets
Total assets	355	71
Liabilities
Total liabilities	31	30
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total assets	281	45
Liabilities
Total liabilities	$ 23	$ 22