Financings (Revolving Credit Facilities) (Details) (USD $)
In Millions, unless otherwise specified
9 Months Ended3 Months Ended
Sep. 30, 2011
Sep. 30, 2011
Consumers Energy Company [Member]
Revolving Credit Facilities March 31, 2016 [Member]
Sep. 30, 2011
Revolving Credit Facilities March 31, 2016 [Member]
Sep. 30, 2011
Consumers Energy Company [Member]
Revolving Credit Facilities August 9, 2013 [Member]
Sep. 30, 2011
Consumers Energy Company [Member]
Revolving Credit Facilities September 21, 2011 [Member]
Mar. 31, 2011
Consumers Energy Company [Member]
Amount of Facility $ 500[1],[2]$ 550[3]$ 150[2]$ 30[2],[4] 
Amount Borrowed  [1],[2] [3] [2] [2],[4] 
Letters of Credit Outstanding 1[1],[2]3[3] 30[2],[4] 
Amount Available 499[1],[2]547[3]150[2]  
Line of Credit Facility, Initiation Date     March 31, 2011
Average borrowings$ 14     
Weighted average interest rate2.22%     
[1]2 On March 31, 2011, Consumers entered into a $500 million secured revolving credit facility with a consortium of banks. This facility has a five-year term and replaces Consumers' revolving credit facility that was set to expire in 2012.
[2]3 Obligations under this facility are secured by FMBs of Consumers.
[3] 1 On March 31, 2011, CMS Energy entered into a $550 million secured revolving credit facility with a consortium of banks. This facility has a five-year term and replaces CMS Energy's revolving credit facility that was set to expire in 2012. Obligations under this facility are secured by Consumers common stock. CMS Energy's average borrowings during the nine months ended September 30, 2011 totaled $14 million, with a weighted-average annual interest rate of 2.22 percent, representing LIBOR plus 2.00 percent
[4]4 Secured revolving letter of credit facility.