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Operating Segment Information - Summary of Segment adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income (Detail) - EUR (€) € in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items] |  |  |  |  |
Adjusted EBITDA | € 151 | € 127 | € 268 | € 220 |
Metal price lag | 20 | 7 | 24 | 20 |
Start-up and development costs | (5) | (5) | (9) | (10) |
Manufacturing system and process transformation costs |  | (1) |  | (1) |
Share based compensation costs | (3) | (1) | (6) | (3) |
Gains on pension plan amendments |  |  |  | 22 |
Depreciation and amortization | (46) | (41) | (90) | (84) |
Restructuring costs |  |  |  | (2) |
Unrealized gains / (losses) on derivatives | 11 | (10) | (43) | 18 |
Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities - net |  | (1) | 1 | (5) |
Losses on disposals | (3) | (1) | (4) | (2) |
Other |  | (1) | 1 |  |
Income (loss) from operations | 125 | 73 | 142 | 173 |
Finance costs - net | (36) | (39) | (70) | (93) |
Share of loss of joint-ventures | (9) | (7) | (12) | (13) | € (29)
Income before income tax | 80 | 27 | 60 | 67 |
Income tax expense | (25) | (12) | (29) | (39) |
Net income (loss) | 55 | 15 | 31 | 28 | € (31)
P&ARP [member] |  |  |  |  |
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items] |  |  |  |  |
Adjusted EBITDA | 75 | 57 | 126 | 98 |
A&T [member] |  |  |  |  |
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items] |  |  |  |  |
Adjusted EBITDA | 43 | 41 | 77 | 69 |
AS&I [member] |  |  |  |  |
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items] |  |  |  |  |
Adjusted EBITDA | 39 | 33 | 75 | 64 |
Start-up and development costs | 0 |  | 9 | 7 |
Holdings & Corporate [member] |  |  |  |  |
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items] |  |  |  |  |
Adjusted EBITDA | € (6) | € (4) | € (10) | € (11) |

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