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Derivative Instruments (Assets and Liabilities Fair Value of Derivative Instruments) (Details) (USD $) In Millions | Sep. 30, 2011 | Dec. 31, 2010
--- | --- | ---
Impact of master netting arrangements less than | $ 1 |  | $ 1 |
Impact of cash margin deposits on derivative liabilities less than | 1 |  | 1 |
Consumers Energy Company [Member] | Other Assets [Member] | Commodity Contracts [Member] |  |  |  |
Derivative Assets | 2 |  | 1 |
Other Assets [Member] | Commodity Contracts [Member] |  |  |  |
Derivative Assets | 2 | [1] | 1 | [1]
Consumers Energy Company [Member] | Other Liabilities [Member] | Commodity Contracts [Member] |  |  |  |
Derivative Liabilities |  |  |  |
Other Liabilities [Member] | Commodity Contracts [Member] |  |  |  |
Derivative Liabilities | $ 3 | [2] | $ 4 | [2]
[1] | 1 Assets and liabilities are presented gross and exclude the impact of offsetting derivative assets and liabilities under master netting agreements, which was less than $1 million at September 30, 2011 and December 31, 2010.
[2] | 2 Liabilities exclude the impact of offsetting cash margin deposits paid by CMS ERM to other parties, which was less than $1 million at September 30, 2011 and December 31, 2010. CMS Energy presents these liabilities net of these impacts on its consolidated balance sheets.

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- Definition The amount of cash margin deposits paid to other parties that in accordance with the entity's accounting policy were offset against the gross derivative liability after accounting for master netting arrangements in arriving at the net amount recorded as a liability. + Details
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Balance Type: | credit
Period Type: | instant

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- Definition The impact of offsetting derivative assets and liabilities under master netting arrangements in determining the net amount of derivative assets and liabilities recorded on the balance sheet. + Details
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Period Type: | instant

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- Definition Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959 + Details
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- Definition Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959 + Details
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