Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets
Restricted cash and cash equivalents	$ 27	$ 17
Derivative instruments	0	1
Liabilities
Derivative instruments	19	8
Consumers Energy Company
Assets
Restricted cash and cash equivalents	24	17
Derivative instruments	0	1
Liabilities
Derivative instruments	0	0
Fair Value, Inputs, Level 1
Assets
Cash equivalents	91	0
Restricted cash and cash equivalents	27	17
Nonqualified deferred compensation plan assets	17	18
Liabilities
Nonqualified deferred compensation plan liabilities	17	18
Fair Value, Inputs, Level 1 | Consumers Energy Company
Assets
Cash equivalents	0	0
Restricted cash and cash equivalents	24	17
Nonqualified deferred compensation plan assets	13	14
Liabilities
Nonqualified deferred compensation plan liabilities	13	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	135	36
Liabilities
Total	36	26
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Assets
Total	38	33
Liabilities
Total	$ 13	$ 14