Reportable Segments (Reconciliation of Assets from Segment to Consolidated) (Details) (USD $)
In Millions
Sep. 30, 2011
Dec. 31, 2010
Plant, property, and equipment, gross$ 14,607$ 14,145
Total Assets15,95815,616
Consumers Energy Company [Member] | Electric Utility [Member]
  
Plant, property, and equipment, gross10,311[1]9,944[1]
Total Assets9,607[1]9,321[1]
Electric Utility [Member]
  
Plant, property, and equipment, gross10,311[1]9,944[1]
Total Assets9,607[1]9,321[1]
Consumers Energy Company [Member] | Gas Utility [Member]
  
Plant, property, and equipment, gross4,149[1]4,063[1]
Total Assets4,852[1]4,614[1]
Gas Utility [Member]
  
Plant, property, and equipment, gross4,149[1]4,063[1]
Total Assets4,852[1]4,614[1]
Enterprises [Member]
  
Plant, property, and equipment, gross109102
Total Assets170191
Consumers Energy Company [Member] | Other [Member]
  
Plant, property, and equipment, gross1515
Total Assets599904
Other [Member]
  
Plant, property, and equipment, gross3836
Total Assets1,3291,490
Consumers Energy Company [Member]
  
Plant, property, and equipment, gross14,47514,022
Total Assets$ 15,058$ 14,839
[1]Amounts include a portion of Consumers' other common assets attributable to both the electric and the gas utility businesses.