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Asset Sales, Discontinued Operations, And Impairment Charges (Asset Sales) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2010
Gains (Losses) on Sales of Assets | $ 1 | $ 6
CMS Generation San Nicolas Company [Member] |  |
Gains (Losses) on Sales of Assets |  | 3
Cost-Method Investment [Member] |  |
Gains (Losses) on Sales of Assets |  | 3
Cost Method Investment Sold Carrying Amount |  | $ 0

X
- Definition This item represents the carrying amount of a cost method investment that has been sold. + References No definition available. + Details
Name: | cms_CostMethodInvestmentSoldCarryingAmount
Namespace Prefix: | cms_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net gain (loss) resulting from the sale, transfer, termination, or other disposition of assets during the period, excluding transactions involving capital leases, assets-held- or available-for-lease, and other real estate owned which, to the extent appropriate, are included in gains (losses) on the disposition of assets in nonoperating income (expense). + References No definition available. + Details
Name: | us-gaap_GainsLossesOnSalesOfAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration