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Finance Costs-Net - Summary of Finance Costs - Net (Parenthetical) (Detail) - EUR (€) € in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2017 | Feb. 28, 2017 | Mar. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Analysis of income and expense [line items] |  |  |  |  |  |
Net loss on settlement of debt |  |  |  | € (91) | € (4) |
Exit fees |  |  |  | € 88 |  |
Unamortized arrangement fees |  |  |  |  | € 2 |
Capitalisation rate |  |  |  | 6.00% | 7.00% | 7.00%
Constellium N.V. Senior Notes [member] |  |  |  |  |  |
Analysis of income and expense [line items] |  |  |  |  |  |
Interest expense on debt instrument |  |  |  | € 136 | € 104 | € 81
Net loss on settlement of debt | € (78) |  |  |  |  |
Muscle Shoals' Senior Notes [member] |  |  |  |  |  |
Analysis of income and expense [line items] |  |  |  |  |  |
Interest expense on debt instrument |  |  |  | 7 | 64 | 64
Net loss on settlement of debt |  | € (13) |  |  |  |
Revolving Credit Facility 1 [member] |  |  |  |  |  |
Analysis of income and expense [line items] |  |  |  |  |  |
Interest expense on debt instrument |  |  |  | € 4 | € 3 | € 4
Muscle Shoals senior unsecured PIK toggle notes [member] |  |  |  |  |  |
Analysis of income and expense [line items] |  |  |  |  |  |
Net loss on settlement of debt |  |  | € (2) |  |  |

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