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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Tax Benefits [Line Items] |  |  |
Interest and penalties | $ 0.0 | $ 0.0 | $ 0.0
IRS audit, adjustments to income tax expense | 0.0 |  |
Consumers Energy Company [Member] |  |  |
Income Tax Benefits [Line Items] |  |  |
Reduction of income tax expense | 39.0 | 39.0 | 39.0
Interest and penalties | 0.0 | $ 0.0 | $ 0.0
IRS audit, adjustments to income tax expense | $ 0.0 |  |

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- Definition The period reduction to income tax expense due to the accelerated return of income tax benefits to customers per regulatory treatment + References No definition available. + Details
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- Definition The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319 + Details
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- Definition Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32718-109319 + Details
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