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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) (USD $)
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9 Months Ended |
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Sep. 30, 2013
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Debt Issuance [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | $ 1,000,000,000 |
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Debt Issuance [Member] | CMS Energy [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 250,000,000 |
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Debt Issuance [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 750,000,000 |
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Debt Issuance [Member] | Senior Notes 4.70% Due March 2043 [Member] | CMS Energy [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 250,000,000 |
| Interest rate | 4.70% |
| Debt issuance date | March 2013 |
| Maturity date | March 2043 |
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Debt Issuance [Member] | First Mortgage Bonds 3.95% Due May 2043 [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 425,000,000 |
| Interest rate | 3.95% |
| Debt issuance date | May 2013 |
| Maturity date | May 2043 |
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Debt Issuance [Member] | First Mortgage Bonds 3.375% Due August 2023 [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 325,000,000 |
| Interest rate | 3.375% |
| Debt issuance date | August 2013 |
| Maturity date | August 2023 |
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Debt Retirements [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 675,000,000 |
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Debt Retirements [Member] | CMS Energy [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 250,000,000 |
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Debt Retirements [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 425,000,000 |
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Debt Retirements [Member] | Senior Notes 2.750% Due May 2014 [Member] | CMS Energy [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 250,000,000 |
| Interest rate | 2.75% |
| Debt issuance date | September 2013 |
| Maturity date | May 2014 |
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Debt Retirements [Member] | First Mortgage Bonds 6% Due February 2014 [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | 200,000,000 |
| Interest rate | 6.00% |
| Debt issuance date | June 2013 |
| Maturity date | February 2014 |
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Debt Retirements [Member] | First Mortgage Bonds 5% Due March 2015 [Member] | Consumers Energy Company [Member]
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| Debt Instrument [Line Items] | |
| Debt issuance, principal | $ 225,000,000 |
| Interest rate | 5.00% |
| Debt issuance date | June 2013 |
| Maturity date | March 2015 |