Contingencies And Commitments (Guarantees) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 MW		Dec. 31, 2011	Dec. 31, 2010
Consumers Energy Company [Member]
Expiration Date	Various through September 2029
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 30
Carrying Amount	1
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	[1]
Guarantor Obligations, Maximum Exposure, Undiscounted	512	[1]
Carrying Amount	15	[1]
Non-Related Parties [Member]
Purchase Obligations Total	12,326
Purchase Obligations Due in Year One	1,878
Purchase Obligations Due in Year Two	1,084
Purchase Obligations Due in Year Three	934
Purchase Obligations Due in Year Four	869
Purchase Obligations Due in Year Five	853
Purchase Obligations Due After Year Five	6,708
Non-Related Parties [Member] | Consumers Energy Company [Member]
Purchase Obligations Total	12,326
Purchase Obligations Due in Year One	1,878
Purchase Obligations Due in Year Two	1,084
Purchase Obligations Due in Year Three	934
Purchase Obligations Due in Year Four	869
Purchase Obligations Due in Year Five	853
Purchase Obligations Due After Year Five	6,708
Related Parties [Member]
Purchase Obligations Total	1,469
Purchase Obligations Due in Year One	89
Purchase Obligations Due in Year Two	91
Purchase Obligations Due in Year Three	91
Purchase Obligations Due in Year Four	93
Purchase Obligations Due in Year Five	95
Purchase Obligations Due After Year Five	1,010
Related Parties [Member] | Consumers Energy Company [Member]
Purchase Obligations Total	1,469
Purchase Obligations Due in Year One	89
Purchase Obligations Due in Year Two	91
Purchase Obligations Due in Year Three	91
Purchase Obligations Due in Year Four	93
Purchase Obligations Due in Year Five	95
Purchase Obligations Due After Year Five	1,010
MCV PPA [Member] | Consumers Energy Company [Member]
Term of Unrecorded Unconditional Purchase Obligations	35 years
Unrecorded Unconditional Purchase Obligations, Minimum Quantity Required	1,240
Unrecorded Unconditional Purchase Obligation Capacity Charge Per Mwh	10.14
Unrecorded Unconditional Purchase Obligation, Annual Contribution to Renewable Resources Program By Counterparty	5
Unrecorded Unconditional Purchase Obligation, Contract Extension Period	5 years
Unrecorded Unconditional Purchase Obligation, Purchases	319		292	285
Unrecorded Unconditional Purchase Obligation, Estimated Average Capacity and Energy Charges	250
Palisades PPA [Member] | Consumers Energy Company [Member]
Unrecorded Unconditional Purchase Obligation, Purchases	331		311	286
Unrecorded Unconditional Purchase Obligation, Estimated Average Capacity and Energy Charges	$ 360
Unrecorded Unconditional Purchase Obligations, Maximum Quantity	798

[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