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New Accounting Standards (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | --- | ---
Accumulated Deficit |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | $ 8 | $ 0 | $ 33
Retirement benefits liability |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | (11) | 0 | 0
Retirement benefits liability | Accounting Standards Update 2018-02 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | (11) |  |
Consumers Energy Company | Accumulated Other Comprehensive Loss |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | (19) |  |
Consumers Energy Company | Accumulated Deficit |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | 19 | 0 | 0
Consumers Energy Company | Accumulated Deficit | Accounting Standards Update 2016-01 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | 19 |  |
Consumers Energy Company | Retirement benefits liability |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | (5) | $ 0 | $ 0
Consumers Energy Company | Retirement benefits liability | Accounting Standards Update 2018-02 |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect of change in accounting principle | $ (5) |  |

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