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Income Taxes (Narrative) (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Income Tax Benefits [Line Items] |  |  |
Increase to income tax expense | $ 5,000,000 |  |
Increase (decrease) to deferred income tax expense related to tax rate changes |  | $ 148,000,000 |
Increase (decrease) to deferred tax liabilities related to tax rate changes |  | 1,300,000,000 |
Alternative minimum tax, recovery period | 4 years |  |
Valuation allowance | $ 8,000,000 | 15,000,000 |
Alternative minimum tax credit reclassification | 68,000,000 |  |
Interest and penalties | 0 | 0 | $ 0
General business credits |  |  |
Income Tax Benefits [Line Items] |  |  |
Valuation allowance - general business credits | 3,000,000 |  |
Consumers Energy Company |  |  |
Income Tax Benefits [Line Items] |  |  |
Increase to income tax expense | 1,000,000 |  |
Net regulatory tax liability | 3,836,000,000 | 3,795,000,000 |
Increase (decrease) to deferred income tax expense related to tax rate changes |  | 33,000,000 |
Interest and penalties | 0 | 0 | $ 0
Local Tax Authority |  |  |
Income Tax Benefits [Line Items] |  |  |
Valuation allowance - loss carryforward | 2,000,000 |  |
Federal Tax Authority | Capital Loss Carryforward |  |  |
Income Tax Benefits [Line Items] |  |  |
Valuation allowance - general business credits | 3,000,000 |  |
CMS Energy |  |  |
Income Tax Benefits [Line Items] |  |  |
Increase (decrease) to deferred tax assets related to tax rate changes |  | 239,000,000 |
Tax Years 2008-2011 | State Tax Authority |  |  |
Income Tax Benefits [Line Items] |  |  |
Proceeds from income tax refunds | $ 1,000,000 |  |
Income taxes, net | Consumers Energy Company |  |  |
Income Tax Benefits [Line Items] |  |  |
Net regulatory tax liability |  | $ 1,600,000,000 |

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