Contingencies and Commitments (Guarantees) (Details) (USD $)
In Millions
9 Months Ended
Sep. 30, 2011
Indemnity obligations from asset sales and other agreements [Member]
 
Expiration DateVarious through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted$ 512[1]
Carrying Amount21
CMS Land [Member]
 
Carrying Amount1
Guarantees and put options [Member]
 
Expiration DateVarious through March 2021
Guarantor Obligations, Maximum Exposure, Undiscounted63[2]
Carrying Amount1[2]
Consumers Energy Company [Member]
 
Expiration DateVarious through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted30
Carrying Amount$ 1
[1]1 The majority of this amount arises from stock and asset sale agreements under which CMS Energy or a subsidiary of CMS Energy, other than Consumers, indemnified the purchaser for losses resulting from various matters, including claims related to tax disputes, claims related to PPAs, and defects in title to the assets or stock sold to the purchaser by CMS Energy subsidiaries. Except for items described elsewhere in this note, CMS Energy believes the likelihood of material loss to be remote for the indemnity obligations not recorded as liabilities.
[2]2 At September 30, 2011, the carrying amount of CMS Land's put option agreements with certain Bay Harbor property owners was $1 million. If CMS Land is required to purchase a Bay Harbor property under a put option agreement, it may sell the property to recover the amount paid under the put option agreement.