Financings and Capitalization (Debt Maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 347
Long-term Debt, Maturities, Repayments of Principal in Year Two	583
Long-term Debt, Maturities, Repayments of Principal in Year Three	738
Long-term Debt, Maturities, Repayments of Principal in Year Four	563
Long-term Debt, Maturities, Repayments of Principal in Year Five	630
Consumers Energy Company [Member]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	41
Long-term Debt, Maturities, Repayments of Principal in Year Two	243
Long-term Debt, Maturities, Repayments of Principal in Year Three	324
Long-term Debt, Maturities, Repayments of Principal in Year Four	350
Long-term Debt, Maturities, Repayments of Principal in Year Five	$ 350

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 10

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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- Definition

Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year.

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Amount of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year.

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