Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets
Restricted cash equivalents	$ 18	$ 17
Derivative instruments	3	1
Liabilities
Derivative instruments	10	11
Consumers Energy Company
Assets
Restricted cash equivalents	16	15
Derivative instruments	3	1
Liabilities
Derivative instruments	1	0
Fair Value, Inputs, Level 1
Assets
Restricted cash equivalents	18	17
Nonqualified deferred compensation plan assets	25	23
Liabilities
Nonqualified deferred compensation plan liabilities	25	23
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Restricted cash equivalents	16	15
Nonqualified deferred compensation plan assets	19	18
Liabilities
Nonqualified deferred compensation plan liabilities	19	18
Fair Value, Inputs, Level 1, 2 and 3
Assets
Total assets	46	41
Liabilities
Total liabilities	35	34
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total assets	38	34
Liabilities
Total liabilities	$ 20	$ 18