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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