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Reportable Segments (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Segment Reporting Information [Line Items]          
Operating Revenue $ 1,527 $ 1,587 $ 4,805 $ 4,759  
Net Income Attributable to CMS Energy 172 186 463 474  
Plant, property, and equipment, gross 21,966   21,966   $ 21,010
Total Assets 22,120   22,120   21,622
Consumers Energy Company [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 1,437 1,498 4,536 4,514  
Net income available to common stockholder 181 195 495 498  
Plant, property, and equipment, gross 21,784   21,784   20,838
Total Assets 20,380   20,380   19,946
Electric Utility [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 1,247 1,313 3,360 3,348  
Net Income Attributable to CMS Energy 176 191 394 395  
Plant, property, and equipment, gross [1] 15,056   15,056   14,540
Total Assets [1] 13,639   13,639   13,429
Electric Utility [Member] | Consumers Energy Company [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 1,247 1,313 3,360 3,348  
Net income available to common stockholder 176 191 394 395  
Plant, property, and equipment, gross [1] 15,056   15,056   14,540
Total Assets [1] 13,640   13,640   13,430
Gas Utility [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 190 185 1,176 1,166  
Net Income Attributable to CMS Energy 5 3 101 102  
Plant, property, and equipment, gross [1] 6,713   6,713   6,283
Total Assets [1] 6,701   6,701   6,446
Gas Utility [Member] | Consumers Energy Company [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 190 185 1,176 1,166  
Net income available to common stockholder 5 3 101 102  
Plant, property, and equipment, gross [1] 6,713   6,713   6,283
Total Assets [1] 6,701   6,701   6,446
Enterprises [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 58 59 172 156  
Net Income Attributable to CMS Energy 8 8 27 17  
Plant, property, and equipment, gross 164   164   157
Total Assets 280   280   269
Other reconciling items [Member]          
Segment Reporting Information [Line Items]          
Operating Revenue 32 30 97 89  
Net Income Attributable to CMS Energy (17) (16) (59) (40)  
Plant, property, and equipment, gross 33   33   30
Total Assets 1,500   1,500   1,478
Other reconciling items [Member] | Consumers Energy Company [Member]          
Segment Reporting Information [Line Items]          
Net income available to common stockholder   $ 1   $ 1  
Plant, property, and equipment, gross 15   15   15
Total Assets $ 39   $ 39   $ 70
[1] Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.