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Investments Accounted for Under Equity Method - Summary of Share of Joint Ventures (Detail) - EUR (€) € in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of investments accounted for using equity method [line items] |  |  |
Investments accounted for under the equity method | € 1 | € 16 | € 30
Group share of joint venture's profit / (loss) | € (29) | € (14) | € (3)
Constellium-UACJ ABS LLC [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Ownership percentage | 51.00% | 51.00% |
Investments accounted for under the equity method | € (14) | € 15 |
Group share of joint venture's profit / (loss) | € (29) | € (14) |
Rhenaroll S.A. [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Ownership percentage | 49.85% | 49.85% |
Investments accounted for under the equity method | € 1 | € 1 |
Group share [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Investments accounted for under the equity method | (13) | 16 |
Group share of joint venture's profit / (loss) | (29) | € (14) |
Non-current other financial assets [member] |  |  |
Disclosure of investments accounted for using equity method [line items] |  |  |
Investments accounted for under the equity method | € 14 |  |

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- Definition Disclosure Of Investments Accounted For Using Equity Method [Line Items] + References No definition available. + Details
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- Definition The amount of investments accounted for using the equity method. The equity method is a method of accounting whereby the investment is initially recognised at cost and adjusted thereafter for the post-acquisition change in the investor's share of net assets of the investee. The investor's profit or loss includes its share of the profit or loss of the investee. The investor's other comprehensive income includes its share of the other comprehensive income of the investee. [Refer: At cost [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2017-01-01 -Paragraph 24 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2017-03-01&anchor=para_24_a&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph B16 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_B16&doctype=Appendix&seq=2 -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 54 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_54_e&doctype=Standard -URIDate 2017-03-09 + Details
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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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- Definition The entity's share of the profit (loss) of joint ventures accounted for using the equity method. [Refer: Investments accounted for using equity method; Joint ventures [member]; Profit (loss)] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_85&doctype=Standard -URIDate 2017-03-09 + Details
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