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Plant, Property, and Equipment (Schedule of Finite Lived Intangible Assets Amortization Expense) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Finite-Lived Intangible Assets, Amortization Expense | $ 32 | $ 28 | $ 30
Consumers Energy Company [Member] |  |  |
Finite-Lived Intangible Assets, Amortization Expense | 32 | 27 | 30
Software and Software Development Costs [Member] |  |  |
Finite-Lived Intangible Assets, Amortization Expense | 24 | 19 | 22
Software and Software Development Costs [Member] | Consumers Energy Company [Member] |  |  |
Finite-Lived Intangible Assets, Amortization Expense | 24 | 19 | 22
Minimum [Member] |  |  |
Finite-Lived Intangible Assets, Future Amortization Expense | 39 |  |
Minimum [Member] | Consumers Energy Company [Member] |  |  |
Finite-Lived Intangible Assets, Future Amortization Expense | 39 |  |
Maximum [Member] |  |  |
Finite-Lived Intangible Assets, Future Amortization Expense | 50 |  |
Maximum [Member] | Consumers Energy Company [Member] |  |  |
Finite-Lived Intangible Assets, Future Amortization Expense | $ 50 |  |

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- Definition Aggregate amount of intangible asset amortization recognized as expense during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6905858&loc=d3e16323-109275 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition The aggregate estimated amortization expense for succeeding fiscal years for intangible assets subject to amortization. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(3) -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 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6905858&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration