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Income Taxes (Narrative) (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2017 | Dec. 31, 2018
Income Tax Benefits [Line Items] |  |  |
Increase (decrease) to deferred income tax expense related to tax rate changes |  | $ 148,000,000 |
Alternative minimum tax, recovery period | 4 years |  |
Valuation allowance | $ 2,000,000 |  | $ 8,000,000
Alternative minimum tax credit reclassification | 31,000,000 |  |
Interest and penalties | 0 | 0 | 0
Consumers Energy Company |  |  |
Income Tax Benefits [Line Items] |  |  |
Net regulatory tax liability | 3,829,000,000 |  | 3,836,000,000
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 |  |

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- Definition The portion of the valuation allowance pertaining to the deferred tax asset representing potential future taxable deductions from net operating loss carryforwards for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 30 -Paragraph 5 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109238119&loc=d3e30536-109315 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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