Fair Value Measurements (Assets And Liabilties Measured At Fair Value On A Recurring Basis) (Details) - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents [1] $ 153 $ 158
Restricted cash equivalents [1] 28 19
Nonqualified deferred compensation plan assets [1] 11 10
Commodity contracts [1] 2 1
Total [1] 339 336
Nonqualified deferred compensation plan liabilities [1] 11 10
Commodity contracts [1] 1  
Total [1] 12 10
Consumers Energy Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Restricted cash equivalents [1] 28 19
Nonqualified deferred compensation plan assets [1] 8 7
Commodity contracts [1] 2 1
Total [1] 176 162
Nonqualified deferred compensation plan liabilities [1] 8 7
Commodity contracts [1] 1  
Total [1] 9 7
DB SERP [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents [1] 1 2
DB SERP [Member] | Consumers Energy Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents [1] 1 2
DB SERP [Member] | Mutual Fund [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available for sale - Fair Value [1] 144 146
DB SERP [Member] | Mutual Fund [Member] | Consumers Energy Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available for sale - Fair Value [1] 103 104
CMS Energy Common Stock [Member] | Consumers Energy Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Available for sale - Fair Value [1] $ 34 $ 29
[1] All assets and liabilities were classified as Level 1 with the exception of some commodity contracts, which were classified as Level 3.