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New Accounting Standards (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Accounting Standards Update 2018-02 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect of change in accounting principle |  | $ 11
Retained Earnings (Accumulated Deficit) [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect of change in accounting principle | $ 8 |
Consumers Energy Company [Member] | Accounting Standards Update 2016-01 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect of change in accounting principle |  | 19
Consumers Energy Company [Member] | Accounting Standards Update 2018-02 [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect of change in accounting principle |  | $ 5
Consumers Energy Company [Member] | Retained Earnings (Accumulated Deficit) [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Cumulative effect of change in accounting principle | $ 19 |

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