Reportable Segments (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Segment Reporting Information [Line Items]          
Operating Revenue $ 1,445 $ 1,507 $ 4,830 $ 4,583  
Total Net Income Available to Common Stockholders 126 148 350 315  
Total Plant, Property, and Equipment, Gross 16,566   16,566   15,592
Total Assets 16,986   16,986   17,131
Consumers Energy Company [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 1,386 1,448 4,647 4,405  
Total Net Income Available to Common Stockholders 152 162 413 359  
Total Plant, Property, and Equipment, Gross 16,426   16,426   15,456
Total Assets 16,094   16,094   16,275
Electric Utility [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 1,188 1,239 3,175 3,073  
Total Net Income Available to Common Stockholders 156 165 315 297  
Total Plant, Property, and Equipment, Gross 11,652   11,652   11,041
Total Assets 10,412 [1]   10,412 [1]   10,423 [1]
Electric Utility [Member] | Consumers Energy Company [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 1,188 1,239 3,175 3,073  
Total Net Income Available to Common Stockholders 156 165 315 297  
Total Plant, Property, and Equipment, Gross 11,652   11,652   11,041
Total Assets 10,412 [1]   10,412 [1]   10,423 [1]
Gas Utility [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 198 209 1,472 1,332  
Total Net Income Available to Common Stockholders (4) (3) 97 61  
Total Plant, Property, and Equipment, Gross 4,759   4,759   4,400
Total Assets 5,039 [1]   5,039 [1]   5,016 [1]
Gas Utility [Member] | Consumers Energy Company [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 198 209 1,472 1,332  
Total Net Income Available to Common Stockholders (4) (3) 97 61  
Total Plant, Property, and Equipment, Gross 4,759   4,759   4,400
Total Assets 5,039 [1]   5,039 [1]   5,016 [1]
Enterprises [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 44 44 136 136  
Total Net Income Available to Common Stockholders (4) 5 1 9  
Total Plant, Property, and Equipment, Gross 116   116   113
Total Assets 188   188   181
Other [Member]
          
Segment Reporting Information [Line Items]          
Operating Revenue 15 15 47 42  
Total Net Income Available to Common Stockholders (22) (19) (63) (52)  
Total Plant, Property, and Equipment, Gross 39   39   38
Total Assets 1,347   1,347   1,511
Other [Member] | Consumers Energy Company [Member]
          
Segment Reporting Information [Line Items]          
Total Net Income Available to Common Stockholders     1 1  
Total Plant, Property, and Equipment, Gross 15   15   15
Total Assets $ 643   $ 643   $ 836
[1] Amounts include a portion of Consumers’ other common assets attributable to both the electric and gas utility businesses.