Contingencies and Commitments (Contractual Commitments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Consumers Energy Company [Member]
Expiration Date	Various through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 30
Carrying Amount	1
Unrecorded Unconditional Purchase Obligation Capacity Charge Per Mwh	10.14
Guarantees and put options [Member]
Expiration Date	Various through March 2021
Guarantor Obligations, Maximum Exposure, Undiscounted	63	[1]
Carrying Amount	1	[1]
Indemnity obligations from asset sales and other agreements [Member]
Expiration Date	Various through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted	512	[2]
Carrying Amount	17
CMS Land [Member]
Carrying Amount	1
Non-Related Parties [Member] | Consumers Energy Company [Member]
Purchase Obligations Total	14,966
Purchase Obligations Due in Year One	1,868
Purchase Obligations Due in Year Two	1,204
Purchase Obligations Due in Year Three	927
Purchase Obligations Due in Year Four	1,010
Purchase Obligations Due in Year Five	1,010
Purchase Obligations Due After Year Five	8,947
Related Parties [Member] | Consumers Energy Company [Member]
Purchase Obligations Total	1,686
Purchase Obligations Due in Year One	92
Purchase Obligations Due in Year Two	91
Purchase Obligations Due in Year Three	96
Purchase Obligations Due in Year Four	101
Purchase Obligations Due in Year Five	103
Purchase Obligations Due After Year Five	1,203
MCV PPA [Member] | Consumers Energy Company [Member]
Term of Unrecorded Unconditional Purchase Obligation	35-year
Unrecorded Unconditional Purchase Obligation, Minimum Quantity Required	1,240
Unrecorded Unconditional Purchase Obligation, Annual Contribution to Renewable Resources Program By Counterparty	5
Unrecorded Unconditional Purchase Obligation, Contract Extension Period	five years
Unrecorded Unconditional Purchase Obligation, Purchases	292		285	246
Unrecorded Unconditional Purchase Obligation, Estimated Average Capacity and Energy Charges	380
Palisades PPA [Member] | Consumers Energy Company [Member]
Unrecorded Unconditional Purchase Obligation, Purchases	311		286	276
Unrecorded Unconditional Purchase Obligation, Estimated Average Capacity and Energy Charges	$ 340
Unrecorded Unconditional Purchase Obligation, Maximum Quantity	798

[1] At December 31, 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.

[2] 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.