Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents	$ 17	$ 21
Other non-current assets	739	478
Derivative instruments	1	1
Derivative instruments	8	3
Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash and cash equivalents	17	17
Other non-current assets	637	410
Derivative instruments	1	1
Derivative instruments	0	0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	27
Restricted cash and cash equivalents	17	21
Nonqualified deferred compensation plan assets	18	14
Other non-current assets	0	1
Nonqualified deferred compensation plan liabilities	18	14
Level 1 | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Restricted cash and cash equivalents	17	17
Nonqualified deferred compensation plan assets	14	10
Other non-current assets	0	0
Nonqualified deferred compensation plan liabilities	14	10
Fair Value, Inputs, Level 1, 2 and 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	36	64
Total	26	17
Fair Value, Inputs, Level 1, 2 and 3 | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	33	29
Total	14	10
Common Stock | Level 1 | Consumers Energy Company
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
CMS Energy common stock	$ 1	$ 1