Contingencies And Commitments (Guarantees) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Guarantees [Member]
Expiration Date	Various through March 2021
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 60
Carrying Amount	1
Indemnity Obligations From Asset Sales And Other Agreements [Member]
Expiration Date	Various through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted	512	[1]
Carrying Amount	15
Indemnity Obligations From Asset Sales And Other Agreements [Member] | Consumers Energy Company [Member]
Expiration Date	Various through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted	30
Carrying Amount	$ 1

[1] In Millions Maximum Carrying Guarantee DescriptionIssue DateExpiration DateObligation Amount CMS Energy, including ConsumersIndemnity obligations from asset sales   and other agreementsVariousVarious through September 2029$ 512 1 $ 15Guarantees VariousVarious through March 2021 60 1ConsumersIndemnity obligations and other guaranteesVariousVarious through September 2029$ 30$ 1The 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 power purchase agreements, 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