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Investments Accounted for Under Equity Method - Summary of Share of Joint Ventures (Parenthetical) (Detail) - EUR (€) € in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of investments accounted for using equity method [line items] |  |  |
Revenue | € 5,237 | € 4,743 | € 5,153
Constellium-UACJ ABS LLC [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Ownership percentage | 51.00% | 51.00% |
Revenue | € 123 | € 15 |
Rhenaroll S.A. [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Ownership percentage | 49.85% | 49.85% |
Revenue | € 3 | € 3 |

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- Definition The proportion of ownership interest in a joint venture attributable to the entity. [Refer: Joint ventures [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_iv&doctype=Standard -URIDate 2017-03-09 + Details
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