Contingencies And Commitments (Guarantees) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Consumers Energy Company [Member]
Guarantee Description	Indemnity obligations and other guarantees
Expiration Date	Various through September 2029
Maximum obligation	$ 30
Carrying Amount	1
Guarantees [Member]
Guarantee Description	Guarantees
Expiration Date	Various through March 2021
Maximum obligation	57
Carrying Amount	1
Indemnity Obligations From Asset Sales And Other Agreements [Member]
Guarantee Description	Indemnity obligations from asset sales   and other agreements
Expiration Date	Various through September 2029
Maximum obligation	482	[1]
Carrying Amount	$ 15

[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 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.