Financings And Capitalization (Revolving Credit Facilities) (Details) (USD $)
In Millions, unless otherwise specified
 9 Months Ended
Sep. 30, 2013
Revolving Credit Facilities December 21, 2017 [Member] | CMS Energy [Member]
  
Line of Credit Facility [Line Items]  
Expiration Date Dec. 21, 2017 [1]
Amount of Facility $ 550 [1]
Amount Borrowed 25 [1]
Letters of Credit Outstanding 2 [1]
Amount Available 523 [1]
Revolving Credit Facilities December 21, 2017 [Member] | Consumers Energy Company [Member]
  
Line of Credit Facility [Line Items]  
Expiration Date Dec. 21, 2017 [2]
Amount of Facility 500 [2]
Amount Borrowed    [2]
Amount Available 500 [2]
Revolving Credit Facilities April 18, 2017 [Member] | Consumers Energy Company [Member]
  
Line of Credit Facility [Line Items]  
Expiration Date Apr. 18, 2017 [2]
Amount of Facility 150 [2]
Amount Borrowed    [2]
Amount Available 150 [2]
Revolving Credit Facilities September 9, 2014 [Member] | Consumers Energy Company [Member]
  
Line of Credit Facility [Line Items]  
Expiration Date Sep. 09, 2014 [2]
Amount of Facility 30 [2]
Amount Borrowed    [2]
Letters of Credit Outstanding $ 30 [2]
[1] Obligations under this facility are secured by Consumers common stock.
[2] Obligations under this facility are secured by FMBs of Consumers.