Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets
Restricted cash and cash equivalents	$ 17	$ 17
Derivative instruments	3	1
Liabilities
Derivative instruments	21	8
Consumers Energy Company
Assets
Restricted cash and cash equivalents	14	17
Derivative instruments	3	1
Liabilities
Derivative instruments	1	0
Fair Value, Inputs, Level 1
Assets
Cash equivalents	100	0
Restricted cash and cash equivalents	17	17
Nonqualified deferred compensation plan assets	19	18
Liabilities
Nonqualified deferred compensation plan liabilities	19	18
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Cash equivalents	100	0
Restricted cash and cash equivalents	14	17
Nonqualified deferred compensation plan assets	15	14
Liabilities
Nonqualified deferred compensation plan liabilities	15	14
Fair Value, Inputs, Level 1 | Common Stock | Consumers Energy Company
Assets
CMS Energy common stock	1	1
Fair Value, Inputs, Level 1, 2 and 3
Assets
Total	139	36
Liabilities
Total	40	26
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total	133	33
Liabilities
Total	$ 16	$ 14