Constellium SE (CSTM) 6-K 25 Jul 19 2019 Q2 Unaudited Interim Consolidated Income Statement Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2019
Document and entity information [abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Registrant Name	Constellium SE
Entity Central Index Key	0001563411
Current Fiscal Year End Date	--12-31

Unaudited Interim Consolidated

Unaudited Interim Consolidated Income Statement - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Profit or loss [abstract]
Revenue	€ 1,538	€ 1,474	€ 3,074	€ 2,860
Cost of sales	(1,356)	(1,300)	(2,748)	(2,549)
Gross profit	182	174	326	311
Selling and administrative expenses	(70)	(59)	(138)	(117)
Research and development expenses	(12)	(10)	(24)	(21)
Restructuring costs	(1)		(1)
Other gains / (losses) - net	(30)	24	(14)	(23)
Income from operations	69	129	149	150
Finance costs - net	(43)	(40)	(89)	(78)
Share of income / (loss) of joint-ventures		(9)	5	(12)
Income before income tax	26	80	65	60
Income tax expense	(9)	(25)	(24)	(29)
Net income	17	55	41	31
Net income attributable to:
Equity holders of Constellium	16	55	39	31
Non-controlling interests	1		2
Net income	€ 17	€ 55	€ 41	€ 31
Earnings per share attributable to the equity holders of Constellium
Basic	€ 0.12	€ 0.41	€ 0.29	€ 0.23
Diluted	€ 0.11	€ 0.39	€ 0.28	€ 0.22

Unaudited Interim Consolidate_2

Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of comprehensive income [abstract]
Net income	€ 17	€ 55	€ 41	€ 31
Items that will not be reclassified subsequently to the consolidated income statement
Remeasurement on post-employment benefit obligations	(34)	2	(62)	27
Income tax on remeasurement on post-employment benefit obligations	8	(1)	15	(7)
Items that may be reclassified subsequently to the consolidated income statement
Cash flow hedges	2	(23)	(5)	(14)
Net investment hedges	5		4
Income tax on hedges		8	2	5
Currency translation differences	(6)	4	(1)	1
Other comprehensive (loss) / income	(25)	(10)	(47)	12
Total comprehensive (loss) / income	(8)	45	(6)	43
Attributable to:
Equity holders of Constellium	(9)	45	(8)	43
Non-controlling interests	1		2
Total comprehensive (loss) / income	€ (8)	€ 45	€ (6)	€ 43

Unaudited Interim Consolidate_3

Unaudited Interim Consolidated Statement of Financial Position - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	€ 213	€ 164
Trade receivables and other	630	587
Inventories	713	660
Other financial assets	19	30
Total current assets	1,575	1,441
Non-current assets
Property, plant and equipment	1,981	1,666
Goodwill	447	422
Intangible assets	68	70
Investments accounted for under the equity method	1	1
Deferred income tax assets	155	163
Trade receivables and other	67	64
Other financial assets	7	74
Total non-current assets	2,726	2,460
Total Assets	4,301	3,901
Current liabilities
Trade payables and other	1,120	968
Borrowings	162	57
Other financial liabilities	44	60
Income tax payables	9	8
Provisions	22	46
Total current liabilities	1,357	1,139
Non-current liabilities
Trade payables and other	28	27
Borrowings	2,216	2,094
Other financial liabilities	25	29
Pension and other post-employment benefit obligations	672	610
Provisions	95	94
Deferred income tax liabilities	21	22
Total non-current liabilities	3,057	2,876
Total Liabilities	4,414	4,015
Equity
Share capital	3	3
Share premium	420	420
Retained deficit and other reserves	(546)	(545)
Equity attributable to equity holders of Constellium	(123)	(122)
Non-controlling interests	10	8
Total Equity	(113)	(114)
Total Equity and Liabilities	€ 4,301	€ 3,901

Unaudited Interim Consolidate_4

Unaudited Interim Consolidated Statement of Changes in Equity - EUR (€) € in Millions	Total	Share capital [member]	Share premium [member]	Re-measurement [member]	Cash flow and net investment hedges [member]	Foreign currency translation reserve [member]	Other reserves [member]	Retained losses [member]	Total Equity holders of Constellium [member]	Non-controlling interests [member]
Beginning balance (Restated [member]) at Dec. 31, 2017	€ (321)	€ 3	€ 420	€ (147)	€ 13	€ (7)	€ 25	€ (636)	€ (329)	€ 8
Beginning balance at Dec. 31, 2017	(319)	3	420	(147)	13	(7)	25	(634)	(327)	8
Change in accounting policies | Change in accounting policies [member]	(2)							(2)	(2)
Net income	31							31	31
Other comprehensive (loss) / income	12			20	(9)	1			12
Total comprehensive (loss) / income	43			20	(9)	1		31	43
Transactions with equity holders Share-based compensation	6						6		6
Ending balance at Jun. 30, 2018	(272)	3	420	(127)	4	(6)	31	(605)	(280)	8
Beginning balance (Restated [member]) at Dec. 31, 2017	(321)	3	420	(147)	13	(7)	25	(636)	(329)	8
Beginning balance at Dec. 31, 2017	(319)	3	420	(147)	13	(7)	25	(634)	(327)	8
Change in accounting policies | Change in accounting policies [member]	(2)							(2)	(2)
Net income	190							188	188	2
Other comprehensive (loss) / income	7			18	(21)	10			7
Total comprehensive (loss) / income	197			18	(21)	10		188	195	2
Transactions with equity holders Share-based compensation	12						12		12
Transactions with non-controlling interests	(2)									(2)
Ending balance at Dec. 31, 2018	(114)	3	420	(129)	(8)	3	37	(448)	(122)	8
Net income	41							39	39	2
Other comprehensive (loss) / income	(47)			(47)	1	(1)			(47)
Total comprehensive (loss) / income	(6)			(47)	1	(1)		39	(8)	2
Transactions with equity holders Share-based compensation	7						7		7
Ending balance at Jun. 30, 2019	€ (113)	€ 3	€ 420	€ (176)	€ (7)	€ 2	€ 44	€ (409)	€ (123)	€ 10

Unaudited Interim Consolidate_5

Unaudited Interim Consolidated Statement of Cash Flows - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of cash flows [abstract]
Net income	€ 41	€ 31
Adjustments:
Depreciation and amortization	117	90
Finance costs - net	89	78
Income tax expense	24	29
Share of (income) / loss of joint-ventures	(5)	12
Unrealized (gains) / losses on derivatives-net and from remeasurement of monetary assets and liabilities - net	(17)	41
Losses on disposal	2	4
Other - net	6	5
Interest paid	(78)	(60)
Income tax paid	(11)	(11)
Change in trade working capital:
Inventories	24	(94)
Trade receivables	(29)	(196)
Trade payables	104	108
Margin calls	5
Change in provisions and pension obligations	(15)	(11)
Other working capital	3	(32)
Net cash flows from / (used in) operating activities	260	(6)
Purchases of property, plant and equipment	(130)	(97)
Acquisitions of subsidiaries, net of cash acquired	(83)
Proceeds from disposals, net of cash	1
Equity contributions and loans to joint-ventures		(13)
Other investing activities	(4)	6
Net cash flows used in investing activities	(216)	(104)
Proceeds from revolving credit facilities and other loans	76	10
Payment of lease liabilities	(70)	(7)
Transactions with non-controlling interests	(2)
Other financing activities		4
Net cash flows from financing activities	4	7
Net increase / (decrease) in cash and cash equivalents	48	(103)
Cash and cash equivalents - beginning of period	164	269
Effect of exchange rate changes on cash and cash equivalents	1
Cash and cash equivalents - end of period	€ 213	€ 166

General Information

General Information	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
General Information	NOTE 1 - GENERAL INFORMATION Constellium is a global leader in the design and manufacture of a broad range of innovative specialty rolled and extruded aluminium products, serving primarily the packaging, aerospace and automotive end-markets. On June 28, 2019, the Company changed its legal form from Naamloze Vennootschap (N.V.) to Societas Europaea (SE) and its name from Constellium N.V. to Constellium SE. Constellium is a public company with limited liability. The business address (head office) of Constellium SE is Tupolevlaan 41-61, Unless the context indicates otherwise, when we refer to “we”, “our”, “us”, “Constellium”, the “Group” and the “Company” in this document, we are referring to Constellium SE and its subsidiaries.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Significant Accounting Policies	NOTE 2 - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES 2.1 Statement of compliance The Unaudited Condensed Interim Consolidated Financial Statements present the Unaudited Interim Consolidated Income Statement, Statement of Comprehensive Income / (Loss) and Statement of Cash Flows for the six months ended June 30, 2019 and 2018; and the Unaudited Interim Consolidated Statement of Financial Position and Changes in Equity as at June 30, 2019 and December 31, 2018. They are prepared in accordance with IAS 34, ‘Interim Financial Reporting’ and with generally accepted accounting principles under International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The Unaudited Condensed Interim Consolidated Financial Statements do not include all the information and disclosures required in the Consolidated Financial Statements. They should be read in conjunction with the Group’s Consolidated Financial Statements for the year ended December 31, 2018, which were approved by the Board of Directors on March 11, 2019. These Unaudited Condensed Interim Consolidated Financial Statements were approved by management on July 22, 2019. 2.2 Basis of preparation In accordance with IAS 1, ‘Presentation of Financial Statements’, the Unaudited Condensed Interim Consolidated Financial Statements are prepared on the assumption that Constellium is a going concern and will continue in operation for the foreseeable future. The Group’s forecasts and projections, taking account of reasonably possible changes in trading performance, including an assessment of the current macroeconomic environment, indicate that the Group should be able to operate within the level of its current facilities and related covenants. Management considers that the going concern assumption is not invalidated by Constellium’s negative equity as at June 30, 2019. The accounting policies adopted in the preparation of the Unaudited Condensed Interim Consolidated Financial Statements are consistent with those followed in the preparation of the Group’s Consolidated Financial Statements for the year ended December 31, 2018, except for the application of the effective tax rate in accordance with IAS 34 ‘Interim Financial Reporting’ and for the adoption of new standards effective as of January 1, 2019. 2.3 Application of new and revised IFRS The Group has applied, for the first time, IFRS 16 - Leases Uncertainty over Income Tax treatment. Several other amendments and interpretations apply for the first time in 2019, but do not have any impact on the Unaudited Condensed Interim Consolidated Financial Statements of the Group. The Group has not early adopted any other standard, interpretation or amendment that has been issued but is not yet effective. IFRS 16 Leases IFRS 16 - Leases Right-of-use The Group recognizes right-of-use Right-of-use right-of-use right-of-use Right-of-use Lease liabilities At the commencement date of the lease, the Group recognizes a lease liability measured at the present value of lease payments to be made over the lease term. The lease payments include fixed payments less any lease incentive receivables, variable lease payments that depend on an index or a rate, and amounts expected to be paid under residual value guarantees. The lease payments also include the exercise price of a purchase option reasonably certain to be exercised by the Group and payments of penalties for terminating a lease, if the lease term reflects the Group exercising the option to terminate. The variable lease payments that do not depend on an index or a rate are recognized as expense in the period in which the event or condition that triggers the payment occurs. In calculating the present value of lease payments, the Group uses the incremental borrowing rate at the lease commencement date if the interest rate implicit in the lease is not readily determinable. After the commencement date, the amount of lease liabilities is increased to reflect the accretion of interest and reduced by the lease payments made. In addition, the carrying amount of lease liabilities is remeasured if there is a modification, a change in the lease term, a change in the in-substance Short-term leases and leases of low-value The Group applies the short-term lease recognition exemption to leases that have a lease term of 12 months or less from the commencement date and do not contain a purchase option. The Group also applies the low-value low-value The standard replaced IAS 17 - Leases low-value non-lease The Group recognized right-of-use Carrying amount Carrying amount (in millions of Euros) December 31, 2018 IFRS 16 impact January 1, 2019 Property, plant and equipment 1,666 102 1,768 Borrowings (2,151 ) (102 ) (2,253 ) As of December 31, 2018, commitments for leases previously accounted for as operating leases amounted to €133 million. The difference compared to the lease liabilities recognized as of January 1, 2019 is primarily explained by the impact of discounting and the recognition of short-term leases and low-value IFRIC 23 Uncertainty over Income Tax treatment This interpretation provides guidance on how to determine an entity’s taxable result where there is uncertainty over whether tax positions taken by an entity will be accepted by the tax authority. The recognition criteria shall be based on the assessment of whether the tax authority will accept a tax treatment, on a more-likely-than-not The Group adopted IFRIC 23 using the cumulative effect method of adoption at the date of initial application. There was no cumulative effect adjustment to the opening balance of retained earnings as of January 1, 2019. The adoption of IFRIC 23 resulted in the reclassification of €20 million from Provisions to Income tax payable and reduction of Deferred income tax assets and current tax receivables. 2.4 Presentation of the operating performance of each operating segment and of the Group In accordance with IFRS 8 - Operating Segments, Constellium’s CODM measures the profitability and financial performance of its operating segments based on Adjusted EBITDA as it illustrates the underlying performance of continuing operations by excluding certain non-recurring non-operating start-up non-recurring 2.5 Principles governing the preparation of the Unaudited Condensed Interim Consolidated Financial Statements The following table summarizes the principal exchange rates used for the preparation of the Unaudited Condensed Interim Consolidated Financial Statements of the Group: Six months ended Six months ended At December 31, June 30, 2019 At June 30, 2019 June 30, 2018 2018 Foreign exchange rate for 1 Euro Average rate Closing rate Average rate Closing rate U.S. Dollars USD 1.1297 1.1380 1.2097 1.1450 Swiss Francs CHF 1.1294 1.1105 1.1696 1.1269 Czech Koruna CZK 25.6842 25.4470 25.4992 25.7240 Presentation of financial statements The Unaudited Condensed Interim Consolidated Financial Statements are presented in millions of Euros, except Earnings per share in Euros. Certain reclassifications may have been made to prior year amounts to conform to the current year presentation. Seasonality of operations Due to the seasonal nature of the Group’s operations, the Group would typically expect higher revenues and operating profits in the first half of the year compared to the second half. 2.6 Judgments in applying accounting policies and key sources of estimation uncertainty The preparation of the Unaudited Condensed Interim Consolidated Financial Statements requires the Group to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Unaudited Condensed Interim Consolidated Financial Statements. Estimates and judgments are continually evaluated and are based on historical experience and other factors, including expectations of future events that are believed to be reasonable under the circumstances. The resulting accounting estimates will, by definition, rarely be equal to the related actual results. Actual results may differ significantly from these estimates, the effect of which is recognized in the period in which the facts that give rise to the revision become known. In preparing these Unaudited Condensed Interim Consolidated Financial Statements, the significant judgments made by management in applying the Group’s accounting policies and the key sources of estimation uncertainty were those applied to the Consolidated Financial Statements at, and for the year ended December 31, 2018. In addition, in accordance with IAS 34, the Group applied, in the preparation of these Unaudited Condensed Interim Consolidated Financial Statements, a projected tax rate for the full year of 2019.

Acquisition of Constellium-Bowl

Acquisition of Constellium-Bowling Green	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Acquisition of Constellium-Bowling Green	NOTE 3 - ACQUISITION OF CONSTELLIUM BOWLING GREEN The acquisition of 49% of Constellium-UACJ ABS LLC was completed on January 10, 2019, strengthening our position in the North American Auto Body Sheet market. The entity was renamed Constellium Bowling Green and is fully consolidated in 2019. Constellium is estimating, on a preliminary basis, the provisional fair values as of January 10, 2019 of the assets acquired and liabilities assumed. These estimated fair values are subject to change, for a maximum 12-month The following table reflects the goodwill arising as a result of the preliminary allocation of purchase price to the Bowling Green assets acquired and liabilities assumed as of January 10, 2019: Estimated Fair (in millions of Euros) Value Cash and cash equivalents 4 Trade receivables and other 49 Inventories 74 Property, plant and equipment 165 Deferred tax assets 1 Trade payables and other (43 ) Borrowings (75 ) Net asset acquired at fair value 175 Preliminary Goodwill 22 Total Consideration 197 Total consideration includes €87 million of cash consideration paid for the 49% stake in Constellium-UACJ ABS LLC, €72 million for the fair value of Constellium’s previously held interest in Constellium-UACJ ABS LLC and €38 million of preexisting trade receivables with Constellium-UACJ ABS LLC. Property, plant and equipment, Inventories, Provisions and Borrowings have been remeasured at fair value. The €22 million of goodwill is the result of expected synergies and will be amortized over 15 years for tax purposes. Considering the industries served, its major customers and product lines, Bowling Green and its related assets and liabilities are included in the Packaging and Automotive Rolled Products (P&ARP) operating segment. Acquisition costs were recognized as expenses in Other gains / (losses) – net in the Unaudited Interim Consolidated Income Statement (€1 million in 2019).

Revenue

Revenue	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Revenue	NOTE 4 - REVENUE Disaggregation of revenue The following table presents our revenue by product line: Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Packaging rolled products 568 589 1,116 1,125 Automotive rolled products 209 163 439 318 Specialty and other thin-rolled products 42 47 90 92 Aerospace rolled products 224 197 429 376 Transportation, Industry and other rolled products 148 148 310 300 Automotive extruded products 199 178 387 347 Other extruded products 148 148 303 296 Other — 4 — 6 Total Revenue 1,538 1,474 3,074 2,860 The following table presents our revenue by destination of shipment: Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 France 154 152 306 302 Germany 339 349 678 700 United Kingdom 49 39 99 83 Switzerland 18 26 38 43 Other Europe 286 270 555 514 United States 600 485 1,164 928 Canada 9 28 27 49 Asia and Other Pacific 68 76 137 143 All Other 15 49 70 98 Total Revenue 1,538 1,474 3,074 2,860 Revenue is recognized at a point in time, except for certain products representing less than 1% of total revenue with no alternative use for which we have a right to payment.

Operating Segment Information

Operating Segment Information	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Operating Segment Information	NOTE 5 - OPERATING SEGMENT INFORMATION Management has defined Constellium’s operating segments based upon the product lines, markets and industries it serves, and prepares and reports operating segment information to Constellium’s chief operating decision maker (CODM) (see NOTE 2 – Summary of Significant Accounting Policies) on that basis. 5.1 Segment Revenue Three months ended Three months ended Six months ended Six months ended June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Inter Inter Inter Inter Segment segment External Segment segment External Segment segment External Segment segment External (in millions of Euros) revenue elimination revenue revenue elimination revenue revenue elimination revenue revenue elimination revenue P&ARP 821 (2 ) 819 801 (2 ) 799 1,649 (4 ) 1,645 1,539 (4 ) 1,535 A&T 383 (11 ) 372 356 (11 ) 345 761 (22 ) 739 699 (23 ) 676 AS&I 347 — 347 327 (1 ) 326 691 (1 ) 690 644 (1 ) 643 Holdings & Corporate (A) — — — 4 — 4 — — — 6 — 6 Total 1,551 (13 ) 1,538 1,488 (14 ) 1,474 3,101 (27 ) 3,074 2,888 (28 ) 2,860 (A) In 2018, Holdings & Corporate segment included revenues from supplying metal to third parties. 5.2 Segment Adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income Three months Three months Six months Six months ended ended ended ended (in millions of Euros) Notes June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 P&ARP 79 75 138 127 A&T 64 47 116 83 AS&I 30 39 59 75 Holdings & Corporate (6 ) (6 ) (11 ) (9 ) Adjusted EBITDA 167 155 302 276 Metal price lag (A) (13 ) 20 (31 ) 24 Start-up (B) (3 ) (5 ) (5 ) (9 ) Bowling Green one-time (C) — — (6 ) — Share-based compensation costs (4 ) (3 ) (7 ) (6 ) Depreciation and amortization 15, 16 (60 ) (46 ) (117 ) (90 ) Restructuring costs (1 ) — (1 ) — Unrealized (losses) / gains on derivatives 6 (14 ) 11 17 (43 ) Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities – net 6 (1 ) — — 1 Losses on disposals 6 (1 ) (3 ) (2 ) (4 ) Other (1 ) — (1 ) 1 Income from operations 69 129 149 150 Finance costs - net 8 (43 ) (40 ) (89 ) (78 ) Share of income / (loss) of joint-ventures — (9 ) 5 (12 ) Income before income tax 26 80 65 60 Income tax expense 10 (9 ) (25 ) (24 ) (29 ) Net income 17 55 41 31 (A) Metal price lag represents the financial impact of the timing difference between when aluminium prices included within Constellium Revenues are established and when aluminium purchase prices included in Cost of sales are established. The Group accounts for inventory using a weighted average price basis and this adjustment aims to remove the effect of volatility in LME prices. The calculation of the Group metal price lag adjustment is based on an internal standardized methodology calculated at each of Constellium’s manufacturing sites and is primarily calculated as the average value of product recorded in inventory, which approximates the spot price in the market, less the average value transferred out of inventory, which is the weighted average of the metal element of cost of sales, based on the quantity sold in the period. (B) For the six months ended June 30, 2019 and 2018, start-up (C) For the six months ended June 30, 2019, Bowling Green one-time non-cash step-up. 5.3 Segment capital expenditures Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 P&ARP (23 ) (17 ) (44 ) (30 ) A&T (16 ) (10 ) (29 ) (23 ) AS&I (31 ) (22 ) (56 ) (42 ) Holdings & Corporate (1 ) (1 ) (1 ) (2 ) Capital expenditures (71 ) (50 ) (130 ) (97 ) 5.4 Segment assets Segment assets are comprised of total assets of Constellium by segment, less deferred income tax assets, cash and cash equivalents and other financial assets. (in millions of Euros) At June 30, At December 31, P&ARP 2,008 1,791 A&T 861 831 AS&I 694 544 Holdings & Corporate 344 304 Segment assets 3,907 3,470 Unallocated: Deferred income tax assets 155 163 Cash and cash equivalents 213 164 Other financial assets 26 104 Total Assets 4,301 3,901

Other Gains _ (Losses)-Net

Other Gains / (Losses)-Net	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Other Gains / (Losses)-Net	NOTE 6 - OTHER GAINS / (LOSSES) – NET (in millions of Euros) Notes Three months Three months Six months Six months Realized (losses) / gains on derivatives (A) (14 ) 15 (28 ) 22 Unrealized (losses) / gains on derivatives at fair value through profit and loss – net (A) 5 (14 ) 11 17 (43 ) Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities – net 5 (1 ) — — 1 Losses on disposal 5 (1 ) (3 ) (2 ) (4 ) Other — 1 (1 ) 1 Total other gains / (losses) – net (30 ) 24 (14 ) (23 ) (A) Realized gains and losses are related to derivatives entered into with the purpose of mitigating exposure to volatility in foreign currencies and commodity prices. Unrealized gains and losses are related to derivatives that do not qualify for hedge accounting.

Currency Gains _ (Losses)

Currency Gains / (Losses)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Currency Gains / (Losses)	NOTE 7 - CURRENCY GAINS / (LOSSES) Currency gains and losses, which are included in Income from operations, are as follows: (in millions of Euros) Notes Three months Three months Six months Six months Included in Revenue 20 (1 ) 1 (2 ) 3 Included in Cost of sales — 2 — — Included in Other (losses) / gains – net (1 ) 3 4 3 Total (2 ) 6 2 6 Realized exchange (losses) / gains on foreign currency derivatives – net 20 — (1 ) 1 1 Unrealized (losses) / gains on foreign currency derivatives – net 20 (1 ) 4 1 3 Exchanges (losses) / gains from the remeasurement of monetary assets and liabilities – net (1 ) 3 — 2 Total (2 ) 6 2 6 See NOTE 19 - Financial Instruments and NOTE 20 - Financial Risk Management for further information regarding the Company’s foreign currency derivatives and hedging activities.

Finance Costs-Net

Finance Costs-Net	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Finance Costs-Net	NOTE 8 - FINANCE COSTS – NET (in millions of Euros) Three months Three months Six months Six months Interest received — 1 — 3 Finance income — 1 — 3 Interest expense on borrowings (A) (30 ) (30 ) (62 ) (58 ) Expenses on factoring arrangements (5 ) (5 ) (10 ) (9 ) Interest expense on lease liabilities (4 ) (1 ) (7 ) (2 ) Realized and unrealized (losses) / gains on debt derivatives at fair value (B) (4 ) 23 5 16 Realized and unrealized exchange gains / (losses) on financing activities – net (B) 6 (22 ) — (11 ) Interest cost on pension and other benefits (4 ) (4 ) (8 ) (8 ) Other finance expenses (C) (2 ) (2 ) (8 ) (11 ) Capitalized borrowing costs (D) — — 1 2 Finance expense (43 ) (41 ) (89 ) (81 ) Finance costs – net (43 ) (40 ) (89 ) (78 ) (A) For the six months ended June 30, 2019, the Group incurred mainly (i) €58 million of interest related to Constellium SE Senior Notes and (ii) €4 million of interest expense and fees related to our North American ABL Facility (“Pan-US Pan-US (B) The Group hedges the dollar exposure relating to the principal of its Constellium SE U.S. Dollar Senior Notes, for the portion that has not been used to finance directly or indirectly U.S. Dollar functional currency entities. Changes in the fair value of these hedging derivatives are recognized within Finance costs—net in the Unaudited Interim Consolidated Income Statement and largely offset the unrealized results related to Constellium SE U.S. Dollar Senior Notes revaluation. (C) For the six months ended June 30, 2018, other finance expenses include a €6 million net loss resulting from the modification of our loan to Constellium-UACJ ABS LLC in February 2018. (D) Borrowing costs directly attributable to the construction of assets are capitalized. The capitalization rate used for the six months ended June 30, 2019 was 6% (6% for the six months ended June 30, 2018).

Share Of Income _ (Loss) Of Joi

Share Of Income / (Loss) Of Joint Ventures	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Share Of Income / (Loss) Of Joint Ventures	NOTE 9 - SHARE OF INCOME / (LOSS) OF JOINT VENTURES The acquisition of 49% of Constellium-UACJ ABS LLC was completed on January 10, 2019 and the entity is fully consolidated since the acquisition date. The remeasurement of the 51% previously held equity interest in Constellium-UACJ ABS LLC at the acquisition date resulted in the recognition of a €5 million profit presented in Share of income / (loss) of joint ventures in the Unaudited Interim Consolidated Income Statement. At June 30, 2018, Constellium-UACJ ABS LLC was accounted for under the Equity method. The information presented hereafter reflects the amounts included in the Unaudited Interim Consolidated Income Statement for the three months and six months ended June 30, 2018 of the relevant entity in accordance with the Group accounting principles and not the Company’s share of those amounts: (in millions of Euros) Three months Six months Revenue 72 118 Cost of sales (82 ) (141 ) Selling and administrative expenses (2 ) (5 ) Loss from operations (12 ) (28 ) Finance costs (A) (5 ) 4 Net loss (17 ) (24 ) (A) Finance costs include a €12 million gain related to the shareholders’ loan modification for the six months ended June 30, 2018.

Income Tax

Income Tax	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Income Tax	NOTE 10 - INCOME TAX Income tax expense is recognized based on the best estimate of the weighted average annual income tax rate expected for the full year. The tax rate applied as at June 30, 2019 is impacted by non-recurring

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2019
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Earnings Per Share	NOTE 11 - EARNINGS PER SHARE Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share 16 55 39 31 Number of shares attributable to equity holders of Constellium Three months Three months Six months Six months ended ended ended ended (number of shares) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Weighted average number of ordinary shares used to calculate basic earnings per share 136,700,491 134,562,177 136,344,030 134,517,869 Effect of other dilutive potential ordinary shares (A) 3,620,938 4,471,455 4,005,235 4,515,005 Weighted average number of ordinary shares used to calculate diluted earnings per share 140,321,429 139,033,632 140,349,265 139,032,874 (A) Dilutive potential new ordinary shares to be issued are part of Share-based compensation plans. Earnings per share attributable to the equity holders of Constellium Three months Three months Six months Six months ended ended ended ended (in Euro per share) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Basic 0.12 0.41 0.29 0.23 Diluted 0.11 0.39 0.28 0.22

Cash and Cash Equivalents

Cash and Cash Equivalents	6 Months Ended
	Jun. 30, 2019
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Cash and Cash Equivalents	NOTE 12 - CASH AND CASH EQUIVALENTS At June 30, At December 31, (in millions of Euros) 2019 2018 Cash in bank and on hand 213 164 Total Cash and cash equivalents 213 164 At June 30, 2019, cash in bank and on hand includes a total of €21 million held by subsidiaries that operate in countries where capital control restrictions prevent the balances from being immediately available for general use by the other entities within the Group (€18 million at December 31, 2018).

Trade Receivables and Other

Trade Receivables and Other	6 Months Ended
	Jun. 30, 2019
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Trade Receivables and Other	NOTE 13 - TRADE RECEIVABLES AND OTHER Trade receivables and other are comprised of the following: At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Trade receivables – gross — 523 — 483 Impairment — (2 ) — (2 ) Total Trade receivables – net — 521 — 481 Income tax receivables 27 44 28 43 Other taxes — 26 — 33 Contract assets 30 1 28 2 Prepaid expenses — 16 1 12 Other 10 22 7 16 Total Other receivables 67 109 64 106 Total Trade receivables and Other 67 630 64 587 13.1 Contract assets At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Unbilled tooling costs 29 — 26 — Other 1 1 2 2 Total Contract assets 30 1 28 2 13.2 Aging The aging of total trade receivables - net is as follows: At June 30, At December 31, (in millions of Euros) 2019 2018 Not past due 499 453 1 - 30 days past due 19 23 31 - 60 days past due 1 2 61 - 90 days past due 1 2 Greater than 91 days past due 1 1 Total Trade receivables - net 521 481 Impairment allowance Revisions to the impairment allowance arising from changes in estimates are included as either an additional allowance or recoveries. An allowance of €0.1 million was recognized during the six months ended June 30, 2019 (€0.4 million allowance reversed during the six months ended June 30, 2018). None of the other amounts included in Other receivables were deemed to be impaired. The maximum exposure to credit risk at the reporting date is the carrying value of each class of receivable shown above. The Group does not hold any collateral from its customers or debtors as security. 13.3 Currency concentration The composition of the carrying amounts of total Trade receivables—net by currency is shown in Euro equivalents as follows: At June 30, At December 31, (in millions of Euros) 2019 2018 Euro 230 177 U.S. Dollar 271 284 Swiss franc 7 4 Other currencies 13 16 Total Trade receivables – net 521 481 13.4 Factoring arrangements The Group factors trade receivables in France by entering into factoring agreements with a third party for a maximum capacity of €235 million. This agreement matures on October 29, 2021. The Group factors trade receivables in Germany, Switzerland and the Czech Republic by entering into factoring agreements with a third party for a maximum capacity of €150 million. This agreement matures on October 29, 2021. In addition, the Group sells receivables from one of its German customers under an uncommitted factoring facility whereby receivables sold are confirmed by the customer. Constellium Automotive USA entered into a factoring agreement that provides for the sale of specific trade receivables up to a maximum capacity of $33 million. This agreement matures on December 11, 2019. Muscle Shoals entered into a factoring agreement that provides for the sale of specific trade receivables up to a maximum capacity of $375 million. The agreement matures on January 24, 2020. Under the Group’s factoring agreements, most of the trade receivables are sold without recourse. Where the Group has transferred substantially all the risks and rewards of ownership of the receivables, the receivables are derecognized. Some remaining receivables do not qualify for derecognition under IFRS 9 - Financial Instruments, Under the agreements, at June 30, 2019, the total carrying amount of the original assets factored is €631 million (December 31, 2018: €601 million) of which: • €471 million (December 31, 2018: €446 million) have been derecognized from the Unaudited Interim Consolidated Statement of Financial Position as the Group transferred substantially all of the associated risks and rewards to the factor; • €160 million (December 31, 2018: €155 million) were recognized on the Unaudited Interim Consolidated Statement of Financial Position. There was no debt due to the factor relating to trade receivables sold at June 30, 2019 and December 31, 2018. Covenants The factoring arrangements contain certain customary affirmative and negative covenants, including some relating to the administration and collection of the assigned receivables, the terms of the invoices and the exchange of information, but do not contain maintenance financial covenants. The commitment of the factor to buy receivables under the Muscle Shoals factoring agreement is subject to maintaining certain credit ratings. The Group was in compliance with all applicable covenants at June 30, 2019 and December 31, 2018.

Inventories

Inventories	6 Months Ended
	Jun. 30, 2019
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Inventories	NOTE 14 - INVENTORIES At June 30, At December 31, (in millions of Euros) 2019 2018 Finished goods 186 165 Work in progress 346 347 Raw materials 137 112 Stores and supplies 75 67 Inventories write-down (31 ) (31 ) Total Inventories 713 660 Constellium records inventories at the lower of cost and net realizable value. Any change in the net realizable value adjustment on inventories is included in Cost of sales in the Unaudited Interim Consolidated Income Statement.

Property, Plant and Equipment

Property, Plant and Equipment	6 Months Ended
	Jun. 30, 2019
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Property, Plant and Equipment	NOTE 15 - PROPERTY, PLANT AND EQUIPMENT Land and Machinery and Construction (in millions of Euros) Note Property Rights Buildings Equipment Work in Progress Other Total Net balance at December 31, 2018 18 217 1,227 194 10 1,666 IFRS 16 application — 82 17 — 3 102 Net balance at January 1, 2019 18 299 1,244 194 13 1,768 Property, plant and equipment acquired through business combination 3 — 40 120 4 1 165 Additions — 14 40 99 1 154 Disposals — — (2 ) — — (2 ) Depreciation expense — (12 ) (95 ) — (5 ) (112 ) Transfer during the period — 4 65 (72 ) 2 (1 ) Effects of changes in foreign exchange rates — 2 6 1 — 9 Net balance at June 30, 2019 18 347 1,378 226 12 1,981 Cost 34 492 2,236 232 40 3,034 Less accumulated depreciation and impairment (16 ) (145 ) (858 ) (6 ) (28 ) (1,053 ) Net balance at June 30, 2019 18 347 1,378 226 12 1,981 Right-of-use Right of use assets have been included within the same line item as that within which the corresponding underlying assets would be presented if they were owned. Machinery and (in millions of Euros) Buildings Equipment Other Total Net balance at December 31, 2018 24 53 — 77 IFRS 16 application 82 17 3 102 Net balance at January 1, 2019 (A) 106 70 3 179 Additions 13 13 1 27 Disposals — — — — Depreciation expense (5 ) (8 ) (1 ) (14 ) Effects of changes in foreign exchange rates 1 — — 1 Net balance at June 30, 2019 115 75 3 193 Cost 127 109 4 240 Less accumulated depreciation and impairment (12 ) (34 ) (1 ) (47 ) Net balance at June 30, 2019 115 75 3 193 (A) The IFRS 16 application included assets acquired through finance leases reclassified as right-of-use right-of-use The total expense relating to short-term leases, low value leases and variable leases still recognized as operating expenses was €7 million for the six months ended June 30, 2019.

Intangible Assets (Including Go

Intangible Assets (Including Goodwill)	6 Months Ended
	Jun. 30, 2019
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Intangible Assets (Including Goodwill)	NOTE 16 - INTANGIBLE ASSETS (INCLUDING GOODWILL) Total intangible Computer Customer Work in assets (excluding (in millions of Euros) Notes Goodwill Technology Software relationships Progress Other goodwill) Net balance at January 1, 2019 422 22 18 15 13 2 70 Intangible assets acquired through 3 22 — — — — — — business combination Additions — — — — 1 — 1 Amortization expense — (2 ) (3 ) — — — (5 ) Transfer during the period — — 1 — — — 1 Effects of changes in foreign exchange rates 3 1 — — — — 1 Net balance at June 30, 2019 447 21 16 15 14 2 68 Cost 447 85 67 40 14 2 208 Less accumulated amortization and impairment — (64 ) (51 ) (25 ) — — (140 ) Net balance at June 30, 2019 447 21 16 15 14 2 68

Trade Payables and Other

Trade Payables and Other	6 Months Ended
	Jun. 30, 2019
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Trade Payables and Other	NOTE 17 - TRADE PAYABLES AND OTHER At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Trade payables — 838 — 685 Fixed asset payables — 29 — 30 Employees’ entitlements — 162 — 160 Taxes payable other than income tax — 25 — 16 Contract liabilities 11 59 9 68 Other payables 17 7 18 9 Total Other 28 282 27 283 Total Trade payables and Other 28 1,120 27 968 Contract liabilities At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Deferred tooling revenue 5 — — — Advance payment from customers 4 6 7 9 Unrecognized variable consideration (A) 2 52 2 57 Prepayment — 1 — 2 Total Contract liabilities 11 59 9 68 (A) Unrecognized variable consideration consists of expected volume rebates, discounts, incentives, refunds penalties and price concessions. For the six months ended June 30, 2019, €25 million was recognized in Revenue that related to contract liabilities as of December 31, 2018. Revenue of €30 million generated in the six months ended June 30, 2019 was deferred.

Borrowings

Borrowings	6 Months Ended
	Jun. 30, 2019
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Borrowings	NOTE 18 - BORROWINGS 18.1 Analysis by nature At December 31, (in millions of Euros) At June 30, 2019 2018 Nominal Nominal Value Nominal Effective Value (Arrangement Accrued Carrying Carrying in Currency rate rate In Euros fees) interests value value Secured Pan-U.S. (A) $ 106 Floating 4.43 % 93 — — 93 — (due 2022) Secured Inventory Based Facility (B) — Floating — — — — — — (due 2021) Senior Unsecured Notes Constellium SE $ 400 5.75 % 6.26 % 352 (3 ) 2 351 348 (Issued May 2014, due 2024) Constellium SE € 300 4.63 % 5.16 % 300 (2 ) 2 300 300 (Issued May 2014, due 2021) Constellium SE $ 650 6.63 % 7.13 % 571 (11 ) 13 573 568 (Issued February 2017, due 2025) Constellium SE $ 500 5.88 % 6.26 % 439 (7 ) 10 442 440 (Issued November 2017, due 2026) Constellium SE € 400 4.25 % 4.57 % 400 (6 ) 6 400 399 (Issued November 2017, due 2026) Unsecured Revolving Credit Facility (C) — Floating — — — — — — (due 2021) Lease liabilities — — — 187 — — 187 73 Other loans (D) — — — 31 — 1 32 23 Total Borrowings — — — 2,373 (29 ) 34 2,378 2,151 Of which non-current 2,216 2,094 Of which current 162 57 Constellium SE Senior Notes are guaranteed by certain subsidiaries. (A) On February 20, 2019, the Pan-U.S. (B) On March 15, 2019, the secured Inventory Based Facility maturity was extended to 2021. (C) The Unsecured Revolving Credit Facility has a 7 million borrowing base and is provided by BPI France, a related party. (D) Other loans include €11 million of financial liabilities relating to sale and lease-backs of assets that were considered, in substance, as financing arrangements. 18.2 Movements in borrowings (in millions of Euros) Note Period ended Year ended At December 31, prior period 2,151 2,127 IFRS 16 application 2 102 — At January 1 2,253 2,127 Cash flows Proceeds / (Repayments) from Revolving Credit Facilities and other loans 76 (68 ) Payment of lease liabilities (70 ) (15 ) Non-cash Borrowings assumed through business combination 3 75 — New leases and other loans 23 33 28 Movement in interests accrued 1 12 Deferred arrangement fees 2 2 Effects of changes in foreign exchange rates 8 65 At the end of the period 2,378 2,151 18.3 Currency concentration The composition of the carrying amounts of total borrowings in Euro equivalents is denominated in the currencies shown below: (in millions of Euros) At June 30, At December 31, U.S. Dollar 1,541 1,408 Euro 811 726 Other currencies 26 17 Total borrowings 2,378 2,151 18.4 Covenants The Group was in compliance with all applicable debt covenants at and for the six months ended June 30, 2019 and for the year ended December 31, 2018. Constellium SE Senior Notes The indentures for our outstanding Senior Notes contain customary terms and conditions, including amongst other things, limitations on incurring or guaranteeing additional indebtedness, on paying dividends, on making other restricted payments, on creating restrictions on dividends and other payments to us from certain of our subsidiaries, on incurring certain liens, on selling assets and subsidiary stock, and on merging. Pan-U.S. This facility contains a fixed charge coverage ratio covenant and EBITDA contribution ratio. Evaluation of compliance is only required if the excess availability falls below 10% of the aggregate revolving loan commitment. It also contains customary affirmative and negative covenants, but no maintenance covenants.

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2019
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Financial Instruments	NOTE 19 - FINANCIAL INSTRUMENTS 19.1 Financial assets and liabilities by categories At June 30, 2019 At December 31, 2018 (in millions of Euros) Notes At amortized At Fair Value At Fair Value Total At amortized At Fair Value At Fair Value Total Cash and cash equivalents 12 213 — — 213 164 — — 164 Trade receivables 13 — — 521 521 — — 481 481 Other financial assets — 26 — 26 74 30 — 104 Total financial assets 213 26 521 760 238 30 481 749 At June 30, 2019 At December 31, 2018 (in millions of Euros) Notes At amortized At Fair Value At Fair Value Total At amortized At Fair Value At Fair Value Total Trade payables and fixed assets payables 17 867 — — 867 715 — — 715 Borrowings 18 2,378 — — 2,378 2,151 — — 2,151 Other financial liabilities — 58 11 69 — 79 10 89 Total financial liabilities 3,245 58 11 3,314 2,866 79 10 2,955 The table below details Other financial assets and Other financial liabilities positions: At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Total Non-current Current Total Derivatives 7 19 26 7 23 30 Aluminium and premium future contracts 2 4 6 2 7 9 Energy future contracts — — — — — — Other future contracts — — — — — — Currency commercial contracts 5 12 17 3 12 15 Currency net debt derivatives — 3 3 2 4 6 Loans (A) — — — 67 2 69 Margin call — — — — 5 5 Other financial assets 7 19 26 74 30 104 Derivatives 25 44 69 29 60 89 Aluminium and premium future contracts 5 22 27 6 38 44 Energy future contracts — — — — — — Other future contracts 3 3 6 5 3 8 Currency commercial contracts 10 14 24 7 12 19 Net investment hedge — — — — 4 4 Currency net debt derivatives 7 5 12 11 3 14 Other financial liabilities 25 44 69 29 60 89 (A) Corresponds to a loan facility to Constellium-UACJ ABS LLC at December 31, 2018 19.2 Fair values All derivatives are presented at fair value in the Unaudited Interim Consolidated Statement of Financial Position. The carrying value of the Group’s borrowings at maturity is the redemption value. The fair value of Constellium SE Senior Notes issued in May 2014, February 2017 and November 2017 account for 102%, 104% and 103% respectively of the nominal value and amount to €664 million, €596 million and €866 million, respectively, at June 30, 2019. The fair value was classified as a Level 1 measurement under the fair value hierarchy provided by IFRS 13 – Fair Value Measurement. The fair values of the other financial assets and liabilities approximate their carrying values, as a result of their liquidity or short maturity. 19.3 Valuation hierarchy The following table provides an analysis of derivatives measured at fair value, grouped into levels based on the degree to which the fair value is observable: • Level 1 valuation is based on quoted prices (unadjusted) in active markets for identical financial instruments. It includes aluminium, copper and zinc futures that are traded on the LME. • Level 2 valuation is based on inputs other than quoted prices included within Level 1 that are observable for the assets or liabilities, either directly (i.e. prices) or indirectly (i.e. derived from prices). It includes foreign exchange derivatives. • Level 3 valuation is based on inputs for the asset or liability that are not based on observable market data (unobservable inputs). Trade receivables are classified as a Level 3 measurement under the fair value hierarchy. At June 30, 2019 At December 31, 2018 (in millions of Euros) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Other financial assets - derivatives 5 21 — 26 9 21 — 30 Other financial liabilities - derivatives 32 37 — 69 50 39 — 89 There was no material transfer of derivatives into or out of Level 1, Level 2 or Level 3 during the six months ended June 30, 2019 and the year ended December 31, 2018.

Financial Risk Management

Financial Risk Management	6 Months Ended
	Jun. 30, 2019
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Financial Risk Management	NOTE 20 - FINANCIAL RISK MANAGEMENT The Group’s financial risk management strategy focuses on minimizing the cash flow impacts of volatility in foreign currency exchange rates, metal prices and interest rates, while maintaining the financial flexibility the Group requires in order to successfully execute the Group’s business strategies. Due to Constellium’s capital structure and the nature of its operations, the Group is exposed to the following financial risks: (i) market risk (including foreign exchange risk, commodity price risk and interest rate risk); (ii) credit risk and (iii) liquidity and capital management risk. 20.1 Market risk In 2016, the Group agreed with a major customer for the sale of fabricated metal products in U.S. Dollars to be supplied from a Euro functional currency entity. In line with its hedging policy, the Group entered into significant foreign exchange derivatives that match related highly probable future conversion sales by selling U.S. Dollars against Euros. The Group designated these derivatives for hedge accounting, with total nominal amount of $296 million as of June 30, 2019 ($369 million as of December 31, 2018) and maturities ranging from 2019 to 2022. For hedges that do not qualify for hedge accounting, any mark-to-market The table below details the effect of foreign currency derivatives in the Unaudited Interim Income Statement and the Unaudited Interim Statement of Comprehensive Income / (Loss): Three months Three months Six months Six months ended June 30, ended June 30, ended June 30, ended June 30, (In millions of Euros) Notes 2019 2018 2019 2018 Derivatives that do not qualify for hedge accounting Included in Other gains / (losses) – net Realized gains / (losses) on foreign currency derivatives – net 7 2 (1 ) 4 (2 ) Unrealized (losses) / gains on foreign currency derivatives – net (A) 7 (1 ) 5 1 4 Derivatives that qualify for hedge accounting Included in Revenue Realized (losses) / gains on foreign currency derivatives – net 7 (1 ) 2 (2 ) 4 Unrealized (losses) on foreign currency derivatives – net 7 — (1 ) — (1 ) Included in Other gains / (losses) – net Realized losses on foreign currency derivatives – net 7 (1 ) (2 ) (1 ) (1 ) Unrealized gains / (losses) on foreign currency derivatives – net 7 — — — — Included in other comprehensive income / (loss) Unrealized gains / (losses) on foreign currency derivatives – net 1 (22 ) (7 ) (11 ) Gains / (Losses) reclassified from cash flow hedge reserve to Consolidated Income Statement 1 (1 ) 2 (3 ) (A) Gains or losses on the hedging instruments are expected to offset losses or gains on the underlying hedged forecasted sales that will be reflected in future periods when these sales are recognized. 20.2 Translation exposures Foreign exchange impacts related to the translation to Euro of net investments in foreign subsidiaries, and related revenues and expenses are not hedged as the Group operates in these various countries on permanent basis, except as described below. In June 2018, the Group entered into forward contracts with nominal amount of CHF174 million to hedge the currency risk associated with the translation of the net assets of its Swiss operations into the Group’s presentation currency. The Group designated these derivatives as a net investment hedge. The realized loss of the net investment hedge is included in Currency translation differences within Other comprehensive income for €2.8 million. 20.3 Liquidity and capital risk management The liquidity requirements of the overall Company are funded by drawing on available credit facilities, while the internal management of liquidity is optimized by means of cash pooling agreements and/or intercompany loans and deposits between the Company’s operating entities and central Treasury. At June 30, 2019, the borrowing base for the Pan-U.S. At June 30, 2019, liquidity was €588 million, comprised of €213 million of cash and cash equivalents and €375 million of available undrawn facilities, including the €314 million described above.

Pensions and Other Post-employm

Pensions and Other Post-employment Benefit Obligations	6 Months Ended
	Jun. 30, 2019
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Pensions and Other Post-employment Benefit Obligations	NOTE 21 - PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS 21.1 Actuarial assumptions Pension and other post-employment benefit obligations were updated based on the discount rates applicable at June 30, 2019. At June 30, At December 31, 2019 2018 Switzerland 0.30% 0.80% U.S. Hourly pension 3.60% - 3.70% 4.40% - 4.45% Salaried pension 3.70% 4.45% OPEB 3.65% - 3.85% 4.40% - 4.55% Other benefits 3.40% - 3.65% 4.25% - 4.40% France Retirements 0.85% 1.65% Other benefits 0.65% 1.35% Germany 0.90% 1.70% 21.2 Amounts recognized in the Unaudited Interim Consolidated Statement of Financial Position At June 30, 2019 At December 31, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Present value of funded obligation 745 — 745 674 — 674 Fair value of plan assets (419 ) — (419 ) (380 ) — (380 ) Deficit of funded plans 326 — 326 294 — 294 Present value of unfunded obligation 131 215 346 115 201 316 Net liability arising from defined benefit obligation 457 215 672 409 201 610 21.3 Amounts recognized in the Unaudited Interim Consolidated Income Statement Three months ended June 30, 2019 Three months ended June 30, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Service cost Current service cost (5 ) (1 ) (6 ) (3 ) (2 ) (5 ) Net interest (2 ) (2 ) (4 ) (2 ) (2 ) (4 ) Immediate recognition of gains / (losses) arising over the period — (2 ) (2 ) — — — Administrative expenses — — — (1 ) — (1 ) Total (7 ) (5 ) (12 ) (6 ) (4 ) (10 ) Six months ended June 30, 2019 Six months ended June 30, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Service cost Current service cost (9 ) (3 ) (12 ) (8 ) (3 ) (11 ) Net interest (4 ) (4 ) (8 ) (4 ) (4 ) (8 ) Immediate recognition of gains / (losses) arising over the period — (2 ) (2 ) — — — Administrative expenses (1 ) — (1 ) (1 ) — (1 ) Total (14 ) (9 ) (23 ) (13 ) (7 ) (20 ) 21.4 Movement in net defined benefit obligations At June 30, 2019 Defined benefit obligations Pension Other Plan Net defined (in millions of Euros) benefits benefits Total Assets benefit liability At January 1, 2019 789 201 990 (380 ) 610 Included in the Consolidated Income Statement Current service cost 9 3 12 — 12 Interest cost / (income) 9 4 13 (5 ) 8 Immediate recognition of gains / (losses) arising over the period — 2 2 — 2 Administration expenses — — — 1 1 Included in the Statement of Comprehensive Income / (Loss) Remeasurement due to: - actual return less interest on plan assets — — — (32 ) (32 ) - changes in financial assumptions 77 16 93 — 93 - changes in demographic assumptions — — — — — - experience losses — (1 ) (1 ) — (1 ) Effects of changes in foreign exchange rates 6 1 7 (4 ) 3 Included in the Consolidated Statement of Cash Flows Benefits paid (16 ) (11 ) (27 ) 15 (12 ) Contributions by the Group — — — (12 ) (12 ) Contributions by the plan participants 2 — 2 (2 ) — At June 30, 2019 876 215 1,091 (419 ) 672 21.5 OPEB amendments In the third quarter of 2018, the Group announced a plan to transfer certain participants in the Constellium Rolled Products Ravenswood Retiree Medical and Life Insurance Plan (“the Plan”) from a company sponsored program to a third-party health network that provides similar benefits at a lower cost. The United Steelworkers Local Union 5668 is contesting the changes to the Plan and filed a lawsuit against Constellium Rolled Products Ravenswood, LLC in a federal district court in West Virginia (the “Court”) seeking to enjoin the Plan changes and to compel arbitration. The Court issued an order in December 2018 enjoining the Company from implementing the changes to the Plan pending resolution in arbitration. The Group believes it has a strong legal position and that it is probable that it will ultimately prevail and be able to implement the Plan changes. 21.6 Net defined benefit obligations by country At June 30, 2019 At December 31, 2018 Defined benefit Plan Net defined Defined benefit Plan Net defined (in millions of Euros) obligations assets benefit liability obligations assets benefit liability France 169 (3 ) 166 151 (3 ) 148 Germany 148 (1 ) 147 136 (1 ) 135 Switzerland 280 (194 ) 86 251 (178 ) 73 United States 493 (221 ) 272 451 (198 ) 253 Other countries 1 — 1 1 — 1 Total 1,091 (419 ) 672 990 (380 ) 610

Provisions

Provisions	6 Months Ended
	Jun. 30, 2019
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Provisions	NOTE 22 - PROVISIONS Close down and environmental Restructuring Legal claims and (in millions of Euros) Notes remediation costs costs other costs Total At January 1, 2019 83 3 54 140 IFRIC 23 application 2 — — (20 ) (20 ) Allowance — — 1 1 Amounts used — — (4 ) (4 ) Unused amounts reversed — — (3 ) (3 ) Unwinding of discounts 3 — — 3 Effects of changes in foreign exchange rates — — — — At June 30, 2019 86 3 28 117 Current 5 2 15 22 Non-Current 81 1 13 95 Total Provisions 86 3 28 117 Legal claims and other costs At June 30, At December 31, (in millions of Euros) 2019 2018 Litigation (A) 19 45 Disease claims 4 4 Other 5 5 Total Provisions for legal claims and other costs 28 54 (A) Decrease in provisions for litigation is mainly explained by the €20 million reclassification upon the adoption of IFRIC 23. Contingencies The Group is involved, and may become involved, in various lawsuits, claims and proceedings relating to customer claims, product liability, and other commercial matters. The Group records provisions for pending litigation matters when it determines that it is probable that an outflow of resources will be required to settle the obligation, and such amounts can be reasonably estimated. In some proceedings, the issues raised are or can be highly complex and subject to significant uncertainties and amounts claimed are and can be substantial. As a result, the probability of loss and an estimation of damages are and can be difficult to ascertain. In exceptional cases, when the Group considers that disclosures relating to provisions and contingencies may prejudice its position, disclosures are limited to the general nature of the dispute The Group is currently subject to an arbitration by a customer claiming that Constellium supplied defective products as a result of which the customer alleges it has suffered significant damages. The Group considers that the claim is without merit on both technical and legal grounds and is vigorously defending the action. For this matter and in respect of others which the Group considers are without merit, while it is possible that an unfavorable outcome may result, after assessing the information available, the Group has concluded that it is not probable that a loss has been incurred.

Non Cash Investing & Financing

Non Cash Investing & Financing Transactions	6 Months Ended
	Jun. 30, 2019
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Non Cash Investing & Financing Transactions	NOTE 23 - NON-CASH Property, plant and equipment acquired through leases or financed by third parties amounted to €33 million and €1 million for the six months ended June 30, 2019 and 2018. These leases and financings are excluded from the Unaudited Interim Statement of Cash Flow as they are non-cash Fair values of vested Restricted Stock Units and Performance Stock Units amounted to €4 million and €3 million for the six months ended June 30, 2019 and June 30, 2018, respectively. They are excluded from the Unaudited Interim Statement of Cash flows as non-cash

Share Capital

Share Capital	6 Months Ended
	Jun. 30, 2019
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Share Capital	NOTE 24 - SHARE CAPITAL At June 30, 2019, authorized share capital amounts to €8 million and is divided into 400,000,000 Class A ordinary shares, each with a nominal value of €0.02. All shares have the right to one vote. in millions of Euros Number of shares Share capital Share premium At January 1, 2019 135,999,394 3 420 New shares issued (A) 817,627 — — At June 30, 2019 136,817,021 3 420 (A) Constellium SE issued and granted Class A ordinary shares to certain employees related to share-based compensation plans.

Share-Based Compensation

Share-Based Compensation	6 Months Ended
	Jun. 30, 2019
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Share-Based Compensation	NOTE 25 - SHARE-BASED COMPENSATION Description of the plans Performance-Based Restricted Stock Units (equity-settled) In April 2019, the Company granted Restricted Stock Units (RSUs) and Performance Stock Units (PSUs) to selected employees. These units will vest after three years from the grant date if the following conditions are met: • A vesting condition under which the beneficiaries must be continuously employed by the Company through the end of the vesting period (3 years), and • In respect of the PSUs, a performance condition, depending on the Total Stockholder Return (TSR) performance of Constellium shares over the vesting period compared to the TSR of specified indices. PSUs will ultimately vest based on a vesting multiplier which ranges from 0 to 2. The following table lists the inputs to the model used for the PSUs granted in April 2019: Fair value at grant date (in Euros) 10.44 Share price at grant date (in Euros) 7.10 Dividend yield — Expected volatility 52 % Risk-free interest rate (U.S. government bond yield) 2.29 % Model used Monte Carlo The fair value of the RSUs awarded is the quoted market price of Constellium shares at grant date. Expense recognized during the year In accordance with IFRS 2, share-based compensation is recognized as an expense over the vesting period. The estimate of this expense is based upon the fair value of a Class A potential ordinary share at grant date. The total expense related to the potential ordinary shares amounted to €7 million and €6 million for the six months ended June 30, 2019 and June 30, 2018, respectively. Movement of potential shares The following table illustrates the number and movements in shares during the period: Performance Restricted Equity Awards Total Based Shares shares Plan Potential shares At January 1, 2019 3,085,164 1,312,524 57,913 4,455,601 Granted (A) 1,028,342 899,926 46,370 1,974,638 Over-performance (B) 21,802 — — 21,802 Vested (807,665 ) (6,000 ) (42,559 ) (856,224 ) Forfeited (C) (78,806 ) (20,737 ) — (99,543 ) At June 30, 2019 3,248,837 2,185,713 61,724 5,496,274 (A) For PSUs, the number of potential shares granted is presented using a vesting multiplier of 100%. (B) When the achievement of TSR performance exceeds the vesting multiplier of 100%, the additional potential shares are presented as over-performance shares. (C) For potential shares related to PSUs, 78,806 were forfeited following the departure of certain beneficiaries and none were forfeited in relation to the non-fulfilment

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Subsequent Events	NOTE 26 - SUBSEQUENT EVENTS On July 9, 2019, Constellium SE called for redemption €100 million of the €300 million outstanding aggregate principal amount of the 4.625% Senior Notes due 2021. The redemption price for the Notes is 100% of the aggregate principal amount of the Notes redeemed, plus accrued and unpaid interest, if any, to the redemption date. The Company expects the redemption date for the Notes being redeemed to occur on August 8, 2019.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Statement of compliance	2.1 Statement of compliance The Unaudited Condensed Interim Consolidated Financial Statements present the Unaudited Interim Consolidated Income Statement, Statement of Comprehensive Income / (Loss) and Statement of Cash Flows for the six months ended June 30, 2019 and 2018; and the Unaudited Interim Consolidated Statement of Financial Position and Changes in Equity as at June 30, 2019 and December 31, 2018. They are prepared in accordance with IAS 34, ‘Interim Financial Reporting’ and with generally accepted accounting principles under International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The Unaudited Condensed Interim Consolidated Financial Statements do not include all the information and disclosures required in the Consolidated Financial Statements. They should be read in conjunction with the Group’s Consolidated Financial Statements for the year ended December 31, 2018, which were approved by the Board of Directors on March 11, 2019. These Unaudited Condensed Interim Consolidated Financial Statements were approved by management on July 22, 2019.
Basis of preparation	2.2 Basis of preparation In accordance with IAS 1, ‘Presentation of Financial Statements’, the Unaudited Condensed Interim Consolidated Financial Statements are prepared on the assumption that Constellium is a going concern and will continue in operation for the foreseeable future. The Group’s forecasts and projections, taking account of reasonably possible changes in trading performance, including an assessment of the current macroeconomic environment, indicate that the Group should be able to operate within the level of its current facilities and related covenants. Management considers that the going concern assumption is not invalidated by Constellium’s negative equity as at June 30, 2019. The accounting policies adopted in the preparation of the Unaudited Condensed Interim Consolidated Financial Statements are consistent with those followed in the preparation of the Group’s Consolidated Financial Statements for the year ended December 31, 2018, except for the application of the effective tax rate in accordance with IAS 34 ‘Interim Financial Reporting’ and for the adoption of new standards effective as of January 1, 2019.
Application of new and revised IFRS	2.3 Application of new and revised IFRS The Group has applied, for the first time, IFRS 16 - Leases Uncertainty over Income Tax treatment. Several other amendments and interpretations apply for the first time in 2019, but do not have any impact on the Unaudited Condensed Interim Consolidated Financial Statements of the Group. The Group has not early adopted any other standard, interpretation or amendment that has been issued but is not yet effective. IFRS 16 Leases IFRS 16 - Leases Right-of-use The Group recognizes right-of-use Right-of-use right-of-use right-of-use Right-of-use Lease liabilities At the commencement date of the lease, the Group recognizes a lease liability measured at the present value of lease payments to be made over the lease term. The lease payments include fixed payments less any lease incentive receivables, variable lease payments that depend on an index or a rate, and amounts expected to be paid under residual value guarantees. The lease payments also include the exercise price of a purchase option reasonably certain to be exercised by the Group and payments of penalties for terminating a lease, if the lease term reflects the Group exercising the option to terminate. The variable lease payments that do not depend on an index or a rate are recognized as expense in the period in which the event or condition that triggers the payment occurs. In calculating the present value of lease payments, the Group uses the incremental borrowing rate at the lease commencement date if the interest rate implicit in the lease is not readily determinable. After the commencement date, the amount of lease liabilities is increased to reflect the accretion of interest and reduced by the lease payments made. In addition, the carrying amount of lease liabilities is remeasured if there is a modification, a change in the lease term, a change in the in-substance Short-term leases and leases of low-value The Group applies the short-term lease recognition exemption to leases that have a lease term of 12 months or less from the commencement date and do not contain a purchase option. The Group also applies the low-value low-value The standard replaced IAS 17 - Leases low-value non-lease The Group recognized right-of-use Carrying amount Carrying amount (in millions of Euros) December 31, 2018 IFRS 16 impact January 1, 2019 Property, plant and equipment 1,666 102 1,768 Borrowings (2,151 ) (102 ) (2,253 ) As of December 31, 2018, commitments for leases previously accounted for as operating leases amounted to €133 million. The difference compared to the lease liabilities recognized as of January 1, 2019 is primarily explained by the impact of discounting and the recognition of short-term leases and low-value IFRIC 23 Uncertainty over Income Tax treatment This interpretation provides guidance on how to determine an entity’s taxable result where there is uncertainty over whether tax positions taken by an entity will be accepted by the tax authority. The recognition criteria shall be based on the assessment of whether the tax authority will accept a tax treatment, on a more-likely-than-not The Group adopted IFRIC 23 using the cumulative effect method of adoption at the date of initial application. There was no cumulative effect adjustment to the opening balance of retained earnings as of January 1, 2019. The adoption of IFRIC 23 resulted in the reclassification of €20 million from Provisions to Income tax payable and reduction of Deferred income tax assets and current tax receivables.
Presentation of the operating performance of each operating segment and of the Group	2.4 Presentation of the operating performance of each operating segment and of the Group In accordance with IFRS 8 - Operating Segments, Constellium’s CODM measures the profitability and financial performance of its operating segments based on Adjusted EBITDA as it illustrates the underlying performance of continuing operations by excluding certain non-recurring non-operating start-up non-recurring
Principles governing the preparation of the Unaudited Condensed Interim Consolidated Financial Statements	2.5 Principles governing the preparation of the Unaudited Condensed Interim Consolidated Financial Statements The following table summarizes the principal exchange rates used for the preparation of the Unaudited Condensed Interim Consolidated Financial Statements of the Group: Six months ended Six months ended At December 31, June 30, 2019 At June 30, 2019 June 30, 2018 2018 Foreign exchange rate for 1 Euro Average rate Closing rate Average rate Closing rate U.S. Dollars USD 1.1297 1.1380 1.2097 1.1450 Swiss Francs CHF 1.1294 1.1105 1.1696 1.1269 Czech Koruna CZK 25.6842 25.4470 25.4992 25.7240 Presentation of financial statements The Unaudited Condensed Interim Consolidated Financial Statements are presented in millions of Euros, except Earnings per share in Euros. Certain reclassifications may have been made to prior year amounts to conform to the current year presentation. Seasonality of operations Due to the seasonal nature of the Group’s operations, the Group would typically expect higher revenues and operating profits in the first half of the year compared to the second half.
Judgments in applying accounting policies and key sources of estimation uncertainty	2.6 Judgments in applying accounting policies and key sources of estimation uncertainty The preparation of the Unaudited Condensed Interim Consolidated Financial Statements requires the Group to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Unaudited Condensed Interim Consolidated Financial Statements. Estimates and judgments are continually evaluated and are based on historical experience and other factors, including expectations of future events that are believed to be reasonable under the circumstances. The resulting accounting estimates will, by definition, rarely be equal to the related actual results. Actual results may differ significantly from these estimates, the effect of which is recognized in the period in which the facts that give rise to the revision become known. In preparing these Unaudited Condensed Interim Consolidated Financial Statements, the significant judgments made by management in applying the Group’s accounting policies and the key sources of estimation uncertainty were those applied to the Consolidated Financial Statements at, and for the year ended December 31, 2018. In addition, in accordance with IAS 34, the Group applied, in the preparation of these Unaudited Condensed Interim Consolidated Financial Statements, a projected tax rate for the full year of 2019.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2019
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Opening Financial Position Reclassification (IFRS 16 Standard)	Carrying amount Carrying amount (in millions of Euros) December 31, 2018 IFRS 16 impact January 1, 2019 Property, plant and equipment 1,666 102 1,768 Borrowings (2,151 ) (102 ) (2,253 )
Disclosure of Foreign Exchange Rates	The following table summarizes the principal exchange rates used for the preparation of the Unaudited Condensed Interim Consolidated Financial Statements of the Group: Six months ended Six months ended At December 31, June 30, 2019 At June 30, 2019 June 30, 2018 2018 Foreign exchange rate for 1 Euro Average rate Closing rate Average rate Closing rate U.S. Dollars USD 1.1297 1.1380 1.2097 1.1450 Swiss Francs CHF 1.1294 1.1105 1.1696 1.1269 Czech Koruna CZK 25.6842 25.4470 25.4992 25.7240

Acquisition of Constellium-Bo_2

Acquisition of Constellium-Bowling Green (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Preliminary Goodwill Arising as a Result of Preliminary Allocation of Purchase Price to Assets Acquired and Liabilities Assumed	The following table reflects the goodwill arising as a result of the preliminary allocation of purchase price to the Bowling Green assets acquired and liabilities assumed as of January 10, 2019: Estimated Fair (in millions of Euros) Value Cash and cash equivalents 4 Trade receivables and other 49 Inventories 74 Property, plant and equipment 165 Deferred tax assets 1 Trade payables and other (43 ) Borrowings (75 ) Net asset acquired at fair value 175 Preliminary Goodwill 22 Total Consideration 197

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Revenue by Product Line	The following table presents our revenue by product line: Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Packaging rolled products 568 589 1,116 1,125 Automotive rolled products 209 163 439 318 Specialty and other thin-rolled products 42 47 90 92 Aerospace rolled products 224 197 429 376 Transportation, Industry and other rolled products 148 148 310 300 Automotive extruded products 199 178 387 347 Other extruded products 148 148 303 296 Other — 4 — 6 Total Revenue 1,538 1,474 3,074 2,860
Disclosure of geographical areas	The following table presents our revenue by destination of shipment: Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 France 154 152 306 302 Germany 339 349 678 700 United Kingdom 49 39 99 83 Switzerland 18 26 38 43 Other Europe 286 270 555 514 United States 600 485 1,164 928 Canada 9 28 27 49 Asia and Other Pacific 68 76 137 143 All Other 15 49 70 98 Total Revenue 1,538 1,474 3,074 2,860

Operating Segment Information (

Operating Segment Information (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Operating Segment Information	5.1 Segment Revenue Three months ended Three months ended Six months ended Six months ended June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Inter Inter Inter Inter Segment segment External Segment segment External Segment segment External Segment segment External (in millions of Euros) revenue elimination revenue revenue elimination revenue revenue elimination revenue revenue elimination revenue P&ARP 821 (2 ) 819 801 (2 ) 799 1,649 (4 ) 1,645 1,539 (4 ) 1,535 A&T 383 (11 ) 372 356 (11 ) 345 761 (22 ) 739 699 (23 ) 676 AS&I 347 — 347 327 (1 ) 326 691 (1 ) 690 644 (1 ) 643 Holdings & Corporate (A) — — — 4 — 4 — — — 6 — 6 Total 1,551 (13 ) 1,538 1,488 (14 ) 1,474 3,101 (27 ) 3,074 2,888 (28 ) 2,860 (A) In 2018, Holdings & Corporate segment included revenues from supplying metal to third parties.
Summary of Segment adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income	5.2 Segment Adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income Three months Three months Six months Six months ended ended ended ended (in millions of Euros) Notes June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 P&ARP 79 75 138 127 A&T 64 47 116 83 AS&I 30 39 59 75 Holdings & Corporate (6 ) (6 ) (11 ) (9 ) Adjusted EBITDA 167 155 302 276 Metal price lag (A) (13 ) 20 (31 ) 24 Start-up (B) (3 ) (5 ) (5 ) (9 ) Bowling Green one-time (C) — — (6 ) — Share-based compensation costs (4 ) (3 ) (7 ) (6 ) Depreciation and amortization 15, 16 (60 ) (46 ) (117 ) (90 ) Restructuring costs (1 ) — (1 ) — Unrealized (losses) / gains on derivatives 6 (14 ) 11 17 (43 ) Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities – net 6 (1 ) — — 1 Losses on disposals 6 (1 ) (3 ) (2 ) (4 ) Other (1 ) — (1 ) 1 Income from operations 69 129 149 150 Finance costs - net 8 (43 ) (40 ) (89 ) (78 ) Share of income / (loss) of joint-ventures — (9 ) 5 (12 ) Income before income tax 26 80 65 60 Income tax expense 10 (9 ) (25 ) (24 ) (29 ) Net income 17 55 41 31 (A) Metal price lag represents the financial impact of the timing difference between when aluminium prices included within Constellium Revenues are established and when aluminium purchase prices included in Cost of sales are established. The Group accounts for inventory using a weighted average price basis and this adjustment aims to remove the effect of volatility in LME prices. The calculation of the Group metal price lag adjustment is based on an internal standardized methodology calculated at each of Constellium’s manufacturing sites and is primarily calculated as the average value of product recorded in inventory, which approximates the spot price in the market, less the average value transferred out of inventory, which is the weighted average of the metal element of cost of sales, based on the quantity sold in the period. (B) For the six months ended June 30, 2019 and 2018, start-up (C) For the six months ended June 30, 2019, Bowling Green one-time non-cash step-up.
Summary of Segment Capital Expenditures	5.3 Segment capital expenditures Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 P&ARP (23 ) (17 ) (44 ) (30 ) A&T (16 ) (10 ) (29 ) (23 ) AS&I (31 ) (22 ) (56 ) (42 ) Holdings & Corporate (1 ) (1 ) (1 ) (2 ) Capital expenditures (71 ) (50 ) (130 ) (97 )
Summary of Segment Assets	5.4 Segment assets Segment assets are comprised of total assets of Constellium by segment, less deferred income tax assets, cash and cash equivalents and other financial assets. (in millions of Euros) At June 30, At December 31, P&ARP 2,008 1,791 A&T 861 831 AS&I 694 544 Holdings & Corporate 344 304 Segment assets 3,907 3,470 Unallocated: Deferred income tax assets 155 163 Cash and cash equivalents 213 164 Other financial assets 26 104 Total Assets 4,301 3,901

Other Gains _ (Losses)-Net (Tab

Other Gains / (Losses)-Net (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Other Gains/(Losses) Net	(in millions of Euros) Notes Three months Three months Six months Six months Realized (losses) / gains on derivatives (A) (14 ) 15 (28 ) 22 Unrealized (losses) / gains on derivatives at fair value through profit and loss – net (A) 5 (14 ) 11 17 (43 ) Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities – net 5 (1 ) — — 1 Losses on disposal 5 (1 ) (3 ) (2 ) (4 ) Other — 1 (1 ) 1 Total other gains / (losses) – net (30 ) 24 (14 ) (23 ) (A) Realized gains and losses are related to derivatives entered into with the purpose of mitigating exposure to volatility in foreign currencies and commodity prices. Unrealized gains and losses are related to derivatives that do not qualify for hedge accounting.

Currency Gains _ (Losses) (Tabl

Currency Gains / (Losses) (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Currency Gains and Losses Included in Income from Operations	Currency gains and losses, which are included in Income from operations, are as follows: (in millions of Euros) Notes Three months Three months Six months Six months Included in Revenue 20 (1 ) 1 (2 ) 3 Included in Cost of sales — 2 — — Included in Other (losses) / gains – net (1 ) 3 4 3 Total (2 ) 6 2 6 Realized exchange (losses) / gains on foreign currency derivatives – net 20 — (1 ) 1 1 Unrealized (losses) / gains on foreign currency derivatives – net 20 (1 ) 4 1 3 Exchanges (losses) / gains from the remeasurement of monetary assets and liabilities – net (1 ) 3 — 2 Total (2 ) 6 2 6

Finance Costs-Net (Tables)

Finance Costs-Net (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Finance Costs-Net	(in millions of Euros) Three months Three months Six months Six months Interest received — 1 — 3 Finance income — 1 — 3 Interest expense on borrowings (A) (30 ) (30 ) (62 ) (58 ) Expenses on factoring arrangements (5 ) (5 ) (10 ) (9 ) Interest expense on lease liabilities (4 ) (1 ) (7 ) (2 ) Realized and unrealized (losses) / gains on debt derivatives at fair value (B) (4 ) 23 5 16 Realized and unrealized exchange gains / (losses) on financing activities – net (B) 6 (22 ) — (11 ) Interest cost on pension and other benefits (4 ) (4 ) (8 ) (8 ) Other finance expenses (C) (2 ) (2 ) (8 ) (11 ) Capitalized borrowing costs (D) — — 1 2 Finance expense (43 ) (41 ) (89 ) (81 ) Finance costs – net (43 ) (40 ) (89 ) (78 ) (A) For the six months ended June 30, 2019, the Group incurred mainly (i) €58 million of interest related to Constellium SE Senior Notes and (ii) €4 million of interest expense and fees related to our North American ABL Facility (“Pan-US Pan-US (B) The Group hedges the dollar exposure relating to the principal of its Constellium SE U.S. Dollar Senior Notes, for the portion that has not been used to finance directly or indirectly U.S. Dollar functional currency entities. Changes in the fair value of these hedging derivatives are recognized within Finance costs—net in the Unaudited Interim Consolidated Income Statement and largely offset the unrealized results related to Constellium SE U.S. Dollar Senior Notes revaluation. (C) For the six months ended June 30, 2018, other finance expenses include a €6 million net loss resulting from the modification of our loan to Constellium-UACJ ABS LLC in February 2018. (D) Borrowing costs directly attributable to the construction of assets are capitalized. The capitalization rate used for the six months ended June 30, 2019 was 6% (6% for the six months ended June 30, 2018).

Share Of Income _ (Loss) Of J_2

Share Of Income / (Loss) Of Joint Ventures (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Share of Income/ Loss of Joint Ventures	Unaudited Interim Consolidated Income Statement for the three months and six months ended June 30, 2018 of the relevant entity in accordance with the Group accounting principles and not the Company’s share of those amounts: (in millions of Euros) Three months Six months Revenue 72 118 Cost of sales (82 ) (141 ) Selling and administrative expenses (2 ) (5 ) Loss from operations (12 ) (28 ) Finance costs (A) (5 ) 4 Net loss (17 ) (24 ) (A) Finance costs include a €12 million gain related to the shareholders’ loan modification for the six months ended June 30, 2018.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2019
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Earning Per Share	Three months Three months Six months Six months ended ended ended ended (in millions of Euros) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share 16 55 39 31 Number of shares attributable to equity holders of Constellium Three months Three months Six months Six months ended ended ended ended (number of shares) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Weighted average number of ordinary shares used to calculate basic earnings per share 136,700,491 134,562,177 136,344,030 134,517,869 Effect of other dilutive potential ordinary shares (A) 3,620,938 4,471,455 4,005,235 4,515,005 Weighted average number of ordinary shares used to calculate diluted earnings per share 140,321,429 139,033,632 140,349,265 139,032,874 (A) Dilutive potential new ordinary shares to be issued are part of Share-based compensation plans. Earnings per share attributable to the equity holders of Constellium Three months Three months Six months Six months ended ended ended ended (in Euro per share) June 30, 2019 June 30, 2018 June 30, 2019 June 30, 2018 Basic 0.12 0.41 0.29 0.23 Diluted 0.11 0.39 0.28 0.22

Cash and Cash Equivalents (Tabl

Cash and Cash Equivalents (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Cash and Cash Equivalents	At June 30, At December 31, (in millions of Euros) 2019 2018 Cash in bank and on hand 213 164 Total Cash and cash equivalents 213 164

Trade Receivables and Other (Ta

Trade Receivables and Other (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Trade Receivables and Other	Trade receivables and other are comprised of the following: At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Trade receivables – gross — 523 — 483 Impairment — (2 ) — (2 ) Total Trade receivables – net — 521 — 481 Income tax receivables 27 44 28 43 Other taxes — 26 — 33 Contract assets 30 1 28 2 Prepaid expenses — 16 1 12 Other 10 22 7 16 Total Other receivables 67 109 64 106 Total Trade receivables and Other 67 630 64 587
Summary of Contract Assets	At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Unbilled tooling costs 29 — 26 — Other 1 1 2 2 Total Contract assets 30 1 28 2
Summary of Ageing of Total Trade Receivables - Net	The aging of total trade receivables - net is as follows: At June 30, At December 31, (in millions of Euros) 2019 2018 Not past due 499 453 1 - 30 days past due 19 23 31 - 60 days past due 1 2 61 - 90 days past due 1 2 Greater than 91 days past due 1 1 Total Trade receivables - net 521 481
Summary of Carrying Amounts of Total Trade Receivables - Net by Currency	The composition of the carrying amounts of total Trade receivables—net by currency is shown in Euro equivalents as follows: At June 30, At December 31, (in millions of Euros) 2019 2018 Euro 230 177 U.S. Dollar 271 284 Swiss franc 7 4 Other currencies 13 16 Total Trade receivables – net 521 481

Inventories (Tables)

Inventories (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Disclosure of Inventories	At June 30, At December 31, (in millions of Euros) 2019 2018 Finished goods 186 165 Work in progress 346 347 Raw materials 137 112 Stores and supplies 75 67 Inventories write-down (31 ) (31 ) Total Inventories 713 660

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	6 Months Ended
	Jun. 30, 2019
Statement [LineItems]
Summary of Property Plant and Equipment	Land and Machinery and Construction (in millions of Euros) Note Property Rights Buildings Equipment Work in Progress Other Total Net balance at December 31, 2018 18 217 1,227 194 10 1,666 IFRS 16 application — 82 17 — 3 102 Net balance at January 1, 2019 18 299 1,244 194 13 1,768 Property, plant and equipment acquired through business combination 3 — 40 120 4 1 165 Additions — 14 40 99 1 154 Disposals — — (2 ) — — (2 ) Depreciation expense — (12 ) (95 ) — (5 ) (112 ) Transfer during the period — 4 65 (72 ) 2 (1 ) Effects of changes in foreign exchange rates — 2 6 1 — 9 Net balance at June 30, 2019 18 347 1,378 226 12 1,981 Cost 34 492 2,236 232 40 3,034 Less accumulated depreciation and impairment (16 ) (145 ) (858 ) (6 ) (28 ) (1,053 ) Net balance at June 30, 2019 18 347 1,378 226 12 1,981
Right-of-use assets [member]
Statement [LineItems]
Summary of Property Plant and Equipment	Right of use assets have been included within the same line item as that within which the corresponding underlying assets would be presented if they were owned. Machinery and (in millions of Euros) Buildings Equipment Other Total Net balance at December 31, 2018 24 53 — 77 IFRS 16 application 82 17 3 102 Net balance at January 1, 2019 (A) 106 70 3 179 Additions 13 13 1 27 Disposals — — — — Depreciation expense (5 ) (8 ) (1 ) (14 ) Effects of changes in foreign exchange rates 1 — — 1 Net balance at June 30, 2019 115 75 3 193 Cost 127 109 4 240 Less accumulated depreciation and impairment (12 ) (34 ) (1 ) (47 ) Net balance at June 30, 2019 115 75 3 193 (A) The IFRS 16 application included assets acquired through finance leases reclassified as right-of-use right-of-use

Intangible Assets (Including _2

Intangible Assets (Including Goodwill) (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Disclosure of Changes in Intangible Assets and Goodwill	Total intangible Computer Customer Work in assets (excluding (in millions of Euros) Notes Goodwill Technology Software relationships Progress Other goodwill) Net balance at January 1, 2019 422 22 18 15 13 2 70 Intangible assets acquired through 3 22 — — — — — — business combination Additions — — — — 1 — 1 Amortization expense — (2 ) (3 ) — — — (5 ) Transfer during the period — — 1 — — — 1 Effects of changes in foreign exchange rates 3 1 — — — — 1 Net balance at June 30, 2019 447 21 16 15 14 2 68 Cost 447 85 67 40 14 2 208 Less accumulated amortization and impairment — (64 ) (51 ) (25 ) — — (140 ) Net balance at June 30, 2019 447 21 16 15 14 2 68

Trade Payables and Other (Table

Trade Payables and Other (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Detailed Information about Trade Payables and Other	At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Trade payables — 838 — 685 Fixed asset payables — 29 — 30 Employees’ entitlements — 162 — 160 Taxes payable other than income tax — 25 — 16 Contract liabilities 11 59 9 68 Other payables 17 7 18 9 Total Other 28 282 27 283 Total Trade payables and Other 28 1,120 27 968
Detailed information of contract liabilities	At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Non-current Current Deferred tooling revenue 5 — — — Advance payment from customers 4 6 7 9 Unrecognized variable consideration (A) 2 52 2 57 Prepayment — 1 — 2 Total Contract liabilities 11 59 9 68 (A) Unrecognized variable consideration consists of expected volume rebates, discounts, incentives, refunds penalties and price concessions.

Borrowings (Tables)

Borrowings (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Borrowings	At December 31, (in millions of Euros) At June 30, 2019 2018 Nominal Nominal Value Nominal Effective Value (Arrangement Accrued Carrying Carrying in Currency rate rate In Euros fees) interests value value Secured Pan-U.S. (A) $ 106 Floating 4.43 % 93 — — 93 — (due 2022) Secured Inventory Based Facility (B) — Floating — — — — — — (due 2021) Senior Unsecured Notes Constellium SE $ 400 5.75 % 6.26 % 352 (3 ) 2 351 348 (Issued May 2014, due 2024) Constellium SE € 300 4.63 % 5.16 % 300 (2 ) 2 300 300 (Issued May 2014, due 2021) Constellium SE $ 650 6.63 % 7.13 % 571 (11 ) 13 573 568 (Issued February 2017, due 2025) Constellium SE $ 500 5.88 % 6.26 % 439 (7 ) 10 442 440 (Issued November 2017, due 2026) Constellium SE € 400 4.25 % 4.57 % 400 (6 ) 6 400 399 (Issued November 2017, due 2026) Unsecured Revolving Credit Facility (C) — Floating — — — — — — (due 2021) Lease liabilities — — — 187 — — 187 73 Other loans (D) — — — 31 — 1 32 23 Total Borrowings — — — 2,373 (29 ) 34 2,378 2,151 Of which non-current 2,216 2,094 Of which current 162 57 Constellium SE Senior Notes are guaranteed by certain subsidiaries. (A) On February 20, 2019, the Pan-U.S. (B) On March 15, 2019, the secured Inventory Based Facility maturity was extended to 2021. (C) The Unsecured Revolving Credit Facility has a 7 million borrowing base and is provided by BPI France, a related party. (D) Other loans include €11 million of financial liabilities relating to sale and lease-backs of assets that were considered, in substance, as financing arrangements.
Summary of Reconciliation of Movement in Net Borrowings Explanatory	18.2 Movements in borrowings (in millions of Euros) Note Period ended Year ended At December 31, prior period 2,151 2,127 IFRS 16 application 2 102 — At January 1 2,253 2,127 Cash flows Proceeds / (Repayments) from Revolving Credit Facilities and other loans 76 (68 ) Payment of lease liabilities (70 ) (15 ) Non-cash Borrowings assumed through business combination 3 75 — New leases and other loans 23 33 28 Movement in interests accrued 1 12 Deferred arrangement fees 2 2 Effects of changes in foreign exchange rates 8 65 At the end of the period 2,378 2,151
Summary of Composition of Carrying Amounts of Total Borrowings	The composition of the carrying amounts of total borrowings in Euro equivalents is denominated in the currencies shown below: (in millions of Euros) At June 30, At December 31, U.S. Dollar 1,541 1,408 Euro 811 726 Other currencies 26 17 Total borrowings 2,378 2,151

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Financial Assets and Liabilities by Categories	19.1 Financial assets and liabilities by categories At June 30, 2019 At December 31, 2018 (in millions of Euros) Notes At amortized At Fair Value At Fair Value Total At amortized At Fair Value At Fair Value Total Cash and cash equivalents 12 213 — — 213 164 — — 164 Trade receivables 13 — — 521 521 — — 481 481 Other financial assets — 26 — 26 74 30 — 104 Total financial assets 213 26 521 760 238 30 481 749 At June 30, 2019 At December 31, 2018 (in millions of Euros) Notes At amortized At Fair Value At Fair Value Total At amortized At Fair Value At Fair Value Total Trade payables and fixed assets payables 17 867 — — 867 715 — — 715 Borrowings 18 2,378 — — 2,378 2,151 — — 2,151 Other financial liabilities — 58 11 69 — 79 10 89 Total financial liabilities 3,245 58 11 3,314 2,866 79 10 2,955
Summary of Other Financial Assets and Other Financial Liabilities Positions	The table below details Other financial assets and Other financial liabilities positions: At June 30, 2019 At December 31, 2018 (in millions of Euros) Non-current Current Total Non-current Current Total Derivatives 7 19 26 7 23 30 Aluminium and premium future contracts 2 4 6 2 7 9 Energy future contracts — — — — — — Other future contracts — — — — — — Currency commercial contracts 5 12 17 3 12 15 Currency net debt derivatives — 3 3 2 4 6 Loans (A) — — — 67 2 69 Margin call — — — — 5 5 Other financial assets 7 19 26 74 30 104 Derivatives 25 44 69 29 60 89 Aluminium and premium future contracts 5 22 27 6 38 44 Energy future contracts — — — — — — Other future contracts 3 3 6 5 3 8 Currency commercial contracts 10 14 24 7 12 19 Net investment hedge — — — — 4 4 Currency net debt derivatives 7 5 12 11 3 14 Other financial liabilities 25 44 69 29 60 89 (A) Corresponds to a loan facility to Constellium-UACJ ABS LLC at December 31, 2018
Summary of Derivatives Measured at Fair Value	The following table provides an analysis of derivatives measured at fair value, grouped into levels based on the degree to which the fair value is observable: • Level 1 valuation is based on quoted prices (unadjusted) in active markets for identical financial instruments. It includes aluminium, copper and zinc futures that are traded on the LME. • Level 2 valuation is based on inputs other than quoted prices included within Level 1 that are observable for the assets or liabilities, either directly (i.e. prices) or indirectly (i.e. derived from prices). It includes foreign exchange derivatives. • Level 3 valuation is based on inputs for the asset or liability that are not based on observable market data (unobservable inputs). Trade receivables are classified as a Level 3 measurement under the fair value hierarchy. At June 30, 2019 At December 31, 2018 (in millions of Euros) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Other financial assets - derivatives 5 21 — 26 9 21 — 30 Other financial liabilities - derivatives 32 37 — 69 50 39 — 89

Financial Risk Management (Tabl

Financial Risk Management (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Effect of Foreign Currency Derivatives Impacts in Consolidated Income Statement and Statement of Comprehensive Income/(Loss)	The table below details the effect of foreign currency derivatives in the Unaudited Interim Income Statement and the Unaudited Interim Statement of Comprehensive Income / (Loss): Three months Three months Six months Six months ended June 30, ended June 30, ended June 30, ended June 30, (In millions of Euros) Notes 2019 2018 2019 2018 Derivatives that do not qualify for hedge accounting Included in Other gains / (losses) – net Realized gains / (losses) on foreign currency derivatives – net 7 2 (1 ) 4 (2 ) Unrealized (losses) / gains on foreign currency derivatives – net (A) 7 (1 ) 5 1 4 Derivatives that qualify for hedge accounting Included in Revenue Realized (losses) / gains on foreign currency derivatives – net 7 (1 ) 2 (2 ) 4 Unrealized (losses) on foreign currency derivatives – net 7 — (1 ) — (1 ) Included in Other gains / (losses) – net Realized losses on foreign currency derivatives – net 7 (1 ) (2 ) (1 ) (1 ) Unrealized gains / (losses) on foreign currency derivatives – net 7 — — — — Included in other comprehensive income / (loss) Unrealized gains / (losses) on foreign currency derivatives – net 1 (22 ) (7 ) (11 ) Gains / (Losses) reclassified from cash flow hedge reserve to Consolidated Income Statement 1 (1 ) 2 (3 ) (A) Gains or losses on the hedging instruments are expected to offset losses or gains on the underlying hedged forecasted sales that will be reflected in future periods when these sales are recognized.

Pensions and Other Post-emplo_2

Pensions and Other Post-employment Benefit Obligations (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Actuarial Assumptions	Pension and other post-employment benefit obligations were updated based on the discount rates applicable at June 30, 2019. At June 30, At December 31, 2019 2018 Switzerland 0.30% 0.80% U.S. Hourly pension 3.60% - 3.70% 4.40% - 4.45% Salaried pension 3.70% 4.45% OPEB 3.65% - 3.85% 4.40% - 4.55% Other benefits 3.40% - 3.65% 4.25% - 4.40% France Retirements 0.85% 1.65% Other benefits 0.65% 1.35% Germany 0.90% 1.70%
Summary of Amounts Recognized in the Unaudited Interim Consolidated Statement of Financial Position	21.2 Amounts recognized in the Unaudited Interim Consolidated Statement of Financial Position At June 30, 2019 At December 31, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Present value of funded obligation 745 — 745 674 — 674 Fair value of plan assets (419 ) — (419 ) (380 ) — (380 ) Deficit of funded plans 326 — 326 294 — 294 Present value of unfunded obligation 131 215 346 115 201 316 Net liability arising from defined benefit obligation 457 215 672 409 201 610
Summary of Amounts Recognized in Unaudited Interim Consolidated Income Statement	21.3 Amounts recognized in the Unaudited Interim Consolidated Income Statement Three months ended June 30, 2019 Three months ended June 30, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Service cost Current service cost (5 ) (1 ) (6 ) (3 ) (2 ) (5 ) Net interest (2 ) (2 ) (4 ) (2 ) (2 ) (4 ) Immediate recognition of gains / (losses) arising over the period — (2 ) (2 ) — — — Administrative expenses — — — (1 ) — (1 ) Total (7 ) (5 ) (12 ) (6 ) (4 ) (10 ) Six months ended June 30, 2019 Six months ended June 30, 2018 Pension Other Pension Other (in millions of Euros) Benefits Benefits Total Benefits Benefits Total Service cost Current service cost (9 ) (3 ) (12 ) (8 ) (3 ) (11 ) Net interest (4 ) (4 ) (8 ) (4 ) (4 ) (8 ) Immediate recognition of gains / (losses) arising over the period — (2 ) (2 ) — — — Administrative expenses (1 ) — (1 ) (1 ) — (1 ) Total (14 ) (9 ) (23 ) (13 ) (7 ) (20 )
Details of Movement in Net Defined Benefit Obligations	21.4 Movement in net defined benefit obligations At June 30, 2019 Defined benefit obligations Pension Other Plan Net defined (in millions of Euros) benefits benefits Total Assets benefit liability At January 1, 2019 789 201 990 (380 ) 610 Included in the Consolidated Income Statement Current service cost 9 3 12 — 12 Interest cost / (income) 9 4 13 (5 ) 8 Immediate recognition of gains / (losses) arising over the period — 2 2 — 2 Administration expenses — — — 1 1 Included in the Statement of Comprehensive Income / (Loss) Remeasurement due to: - actual return less interest on plan assets — — — (32 ) (32 ) - changes in financial assumptions 77 16 93 — 93 - changes in demographic assumptions — — — — — - experience losses — (1 ) (1 ) — (1 ) Effects of changes in foreign exchange rates 6 1 7 (4 ) 3 Included in the Consolidated Statement of Cash Flows Benefits paid (16 ) (11 ) (27 ) 15 (12 ) Contributions by the Group — — — (12 ) (12 ) Contributions by the plan participants 2 — 2 (2 ) — At June 30, 2019 876 215 1,091 (419 ) 672
Details of Net Defined Benefit Obligations by Country	21.6 Net defined benefit obligations by country At June 30, 2019 At December 31, 2018 Defined benefit Plan Net defined Defined benefit Plan Net defined (in millions of Euros) obligations assets benefit liability obligations assets benefit liability France 169 (3 ) 166 151 (3 ) 148 Germany 148 (1 ) 147 136 (1 ) 135 Switzerland 280 (194 ) 86 251 (178 ) 73 United States 493 (221 ) 272 451 (198 ) 253 Other countries 1 — 1 1 — 1 Total 1,091 (419 ) 672 990 (380 ) 610

Provisions (Tables)

Provisions (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Changes in Provisions	Close down and environmental Restructuring Legal claims and (in millions of Euros) Notes remediation costs costs other costs Total At January 1, 2019 83 3 54 140 IFRIC 23 application 2 — — (20 ) (20 ) Allowance — — 1 1 Amounts used — — (4 ) (4 ) Unused amounts reversed — — (3 ) (3 ) Unwinding of discounts 3 — — 3 Effects of changes in foreign exchange rates — — — — At June 30, 2019 86 3 28 117 Current 5 2 15 22 Non-Current 81 1 13 95 Total Provisions 86 3 28 117
Summary of Legal Claims and Other Costs	Legal claims and other costs At June 30, At December 31, (in millions of Euros) 2019 2018 Litigation (A) 19 45 Disease claims 4 4 Other 5 5 Total Provisions for legal claims and other costs 28 54 (A) Decrease in provisions for litigation is mainly explained by the €20 million reclassification upon the adoption of IFRIC 23.

Share Capital (Tables)

Share Capital (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Schedule of Share Capital	in millions of Euros Number of shares Share capital Share premium At January 1, 2019 135,999,394 3 420 New shares issued (A) 817,627 — — At June 30, 2019 136,817,021 3 420 (A) Constellium SE issued and granted Class A ordinary shares to certain employees related to share-based compensation plans.

Share-Based Compensation (Table

Share-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Performance-Based RSU	The following table lists the inputs to the model used for the PSUs granted in April 2019: Fair value at grant date (in Euros) 10.44 Share price at grant date (in Euros) 7.10 Dividend yield — Expected volatility 52 % Risk-free interest rate (U.S. government bond yield) 2.29 % Model used Monte Carlo
Summary of Movements in Shares	The following table illustrates the number and movements in shares during the period: Performance Restricted Equity Awards Total Based Shares shares Plan Potential shares At January 1, 2019 3,085,164 1,312,524 57,913 4,455,601 Granted (A) 1,028,342 899,926 46,370 1,974,638 Over-performance (B) 21,802 — — 21,802 Vested (807,665 ) (6,000 ) (42,559 ) (856,224 ) Forfeited (C) (78,806 ) (20,737 ) — (99,543 ) At June 30, 2019 3,248,837 2,185,713 61,724 5,496,274 (A) For PSUs, the number of potential shares granted is presented using a vesting multiplier of 100%. (B) When the achievement of TSR performance exceeds the vesting multiplier of 100%, the additional potential shares are presented as over-performance shares. (C) For potential shares related to PSUs, 78,806 were forfeited following the departure of certain beneficiaries and none were forfeited in relation to the non-fulfilment

General Information - Additiona

General Information - Additional Information (Detail)	Jun. 30, 2019EmployeesFacilitysiteCenter
Disclosure of general information [abstract]
Number of production facilities | Facility	26
Number of administrative and commercial sites | site	3
Number of R&D centers | Center	3
Number of employees | Employees	13,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - EUR (€) € in Millions	Jan. 01, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary of significant accounting policies [line items]
Short-term lease description		A lease term of 12 months or less from the commencement date
Low value lease assets description		Leases of assets with a value below €5,000
Right of use assets	€ 102
Operating lease liability	€ 102
Average incremental borrowing rate	7.60%
Operating leases			€ 133
IFRIC 23 [member]
Summary of significant accounting policies [line items]
Cumulative effect adjustment in retained earnings	€ 0
IFRIC 23 [member] | Reclassifications [member]
Summary of significant accounting policies [line items]
Reclassification in Income tax payable and reduction of Deferred income tax assets and current tax receivables	€ 20

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Opening Financial Position Reclassification (IFRS 16 Standard) (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of reclassifications or changes in presentation [line items]
Property, plant and equipment	€ 1,981	€ 1,768	€ 1,666
Borrowings	€ (2,378)	(2,253)	€ (2,151)	€ (2,127)
Increase (decrease) due to application of IFRS 16 [member]
Disclosure of reclassifications or changes in presentation [line items]
Property, plant and equipment		102
Borrowings		€ (102)

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies - Disclosure of Foreign Exchange Rates (Detail)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
U.S. Dollar [member]
Disclosure of foreign exchange rates [line items]
Average rate	1.1297	1.2097
Closing rate	1.1380		1.1450
Swiss Franc [member]
Disclosure of foreign exchange rates [line items]
Average rate	1.1294	1.1696
Closing rate	1.1105		1.1269
Czech Republic, Koruny [member]
Disclosure of foreign exchange rates [line items]
Average rate	25.6842	25.4992
Closing rate	25.4470		25.7240

Acquisition of Constellium-Bo_3

Acquisition of Constellium-Bowling Green - Additional Information (Detail) - EUR (€) € in Millions	Jan. 10, 2019	Jun. 30, 2019	Dec. 31, 2018
Disclosure of detailed information about business combination [line items]
Preexisting trade receivables with acquiree		€ 521	€ 481
Goodwill		22
Acquisition costs		6
Other (losses) / gains - net [member]
Disclosure of detailed information about business combination [line items]
Acquisition costs		€ 1
Constellium-Bowling Green [member]
Disclosure of detailed information about business combination [line items]
Percentage of voting equity interests acquired	49.00%
Consideration transferred	€ 87
Fair value of previously held interest	72
Preexisting trade receivables with acquiree	38
Goodwill	€ 22
Goodwill amortization period for income tax purposes	15 years

Acquisition of Constellium-Bo_4

Acquisition of Constellium-Bowling Green - Summary of Preliminary Goodwill Arising as a Result of Preliminary Allocation of Purchase Price to Assets Acquired and Liabilities Assumed (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Jan. 10, 2019
Disclosure of detailed information about business combination [line items]
Property, plant and equipment	€ 165
Preliminary Goodwill	€ 22
Constellium-Bowling Green [member]
Disclosure of detailed information about business combination [line items]
Cash and cash equivalents		€ 4
Trade receivables and other		49
Inventories		74
Property, plant and equipment		165
Deferred tax assets		1
Trade payables and other		(43)
Borrowings		(75)
Net asset acquired at fair value		175
Preliminary Goodwill		22
Total Consideration		€ 197

Revenue - Summary of Revenue by

Revenue - Summary of Revenue by Product Line (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of products and services [line items]
Revenue	€ 1,538	€ 1,474	€ 3,074	€ 2,860
Packaging rolled products [member]
Disclosure of products and services [line items]
Revenue	568	589	1,116	1,125
Automotive rolled products [member]
Disclosure of products and services [line items]
Revenue	209	163	439	318
Specialty and other thin-rolled products [member]
Disclosure of products and services [line items]
Revenue	42	47	90	92
Aerospace rolled products [member]
Disclosure of products and services [line items]
Revenue	224	197	429	376
Transportation, Industry and other rolled products [member]
Disclosure of products and services [line items]
Revenue	148	148	310	300
Automotive extruded products [member]
Disclosure of products and services [line items]
Revenue	199	178	387	347
Other extruded products [member]
Disclosure of products and services [line items]
Revenue	€ 148	148	€ 303	296
Other [member]
Disclosure of products and services [line items]
Revenue		€ 4		€ 6

Revenue - Disclosure of geograp

Revenue - Disclosure of geographical areas (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of geographical areas [line items]
Revenue	€ 1,538	€ 1,474	€ 3,074	€ 2,860
France [member]
Disclosure of geographical areas [line items]
Revenue	154	152	306	302
Germany [member]
Disclosure of geographical areas [line items]
Revenue	339	349	678	700
United Kingdom [member]
Disclosure of geographical areas [line items]
Revenue	49	39	99	83
Switzerland [member]
Disclosure of geographical areas [line items]
Revenue	18	26	38	43
Other Europe [member]
Disclosure of geographical areas [line items]
Revenue	286	270	555	514
United States [member]
Disclosure of geographical areas [line items]
Revenue	600	485	1,164	928
Canada [member]
Disclosure of geographical areas [line items]
Revenue	9	28	27	49
Asia and Other Pacific [member]
Disclosure of geographical areas [line items]
Revenue	68	76	137	143
Other countries [member]
Disclosure of geographical areas [line items]
Revenue	€ 15	€ 49	€ 70	€ 98

Revenue - Additional Informatio

Revenue - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019
Performance obligations satisfied over time [member]
Disclosure of geographical areas [line items]
Percentage of payment option over total revenue	1.00%

Operating Segment Information -

Operating Segment Information - Summary of Segment Revenue (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of operating segments [line items]
Revenue	€ 1,538	€ 1,474	€ 3,074	€ 2,860
P&ARP [member]
Disclosure of operating segments [line items]
Revenue	819	799	1,645	1,535
A&T [member]
Disclosure of operating segments [line items]
Revenue	372	345	739	676
AS&I [member]
Disclosure of operating segments [line items]
Revenue	347	326	690	643
Holdings & Corporate [member]
Disclosure of operating segments [line items]
Revenue		4		6
Segment [member]
Disclosure of operating segments [line items]
Revenue	1,551	1,488	3,101	2,888
Segment [member] | P&ARP [member]
Disclosure of operating segments [line items]
Revenue	821	801	1,649	1,539
Segment [member] | A&T [member]
Disclosure of operating segments [line items]
Revenue	383	356	761	699
Segment [member] | AS&I [member]
Disclosure of operating segments [line items]
Revenue	347	327	691	644
Segment [member] | Holdings & Corporate [member]
Disclosure of operating segments [line items]
Revenue		4		6
Inter segment [member]
Disclosure of operating segments [line items]
Revenue	(13)	(14)	(27)	(28)
Inter segment [member] | P&ARP [member]
Disclosure of operating segments [line items]
Revenue	(2)	(2)	(4)	(4)
Inter segment [member] | A&T [member]
Disclosure of operating segments [line items]
Revenue	€ (11)	(11)	(22)	(23)
Inter segment [member] | AS&I [member]
Disclosure of operating segments [line items]
Revenue		€ (1)	€ (1)	€ (1)

Operating Segment Information_2

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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	€ 167	€ 155	€ 302	€ 276
Metal price lag	(13)	20	(31)	24
Start-up and development costs	(3)	(5)	(5)	(9)
Bowling Green one-time costs related to the acquisition			(6)
Share-based compensation costs	(4)	(3)	(7)	(6)
Depreciation and amortization	(60)	(46)	(117)	(90)
Restructuring costs	(1)		(1)
Unrealized (losses) / gains on derivatives	(14)	11	17	(43)
Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities - net	(1)			1
Losses on disposals	(1)	(3)	(2)	(4)
Other	(1)		(1)	1
Income from operations	69	129	149	150
Finance costs - net	(43)	(40)	(89)	(78)
Share of income / (loss) of joint-ventures		(9)	5	(12)
Income before income tax	26	80	65	60
Income tax expense	(9)	(25)	(24)	(29)
Net income	17	55	41	31	€ 190
P&ARP [member]
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	79	75	138	127
A&T [member]
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	64	47	116	83
AS&I [member]
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	30	39	59	75
Start-up and development costs			5	9
Holdings & Corporate [member]
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	€ (6)	€ (6)	€ (11)	€ (9)

Operating Segment Information_3

Operating Segment Information - Summary of Segment adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income (Parenthetical) (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Start-up costs and development cost	€ (3)	€ (5)	€ (5)	€ (9)
AS&I [member]
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Start-up costs and development cost			€ 5	€ 9

Operating Segment Information_4

Operating Segment Information - Summary of Segment Capital Expenditures (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of operating segments [line items]
Segment capital expenditures	€ (71)	€ (50)	€ (130)	€ (97)
P&ARP [member]
Disclosure of operating segments [line items]
Segment capital expenditures	(23)	(17)	(44)	(30)
A&T [member]
Disclosure of operating segments [line items]
Segment capital expenditures	(16)	(10)	(29)	(23)
AS&I [member]
Disclosure of operating segments [line items]
Segment capital expenditures	(31)	(22)	(56)	(42)
Holdings & Corporate [member]
Disclosure of operating segments [line items]
Segment capital expenditures	€ (1)	€ (1)	€ (1)	€ (2)

Operating Segment Information_5

Operating Segment Information - Summary of Segment Assets (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of operating segments [line items]
Total Assets	€ 4,301	€ 3,901
Deferred income tax assets	155	163
Cash and cash equivalents	213	164	€ 269
Other financial assets	26	104
Segment [member]
Disclosure of operating segments [line items]
Total Assets	3,907	3,470
Segment [member] | P&ARP [member]
Disclosure of operating segments [line items]
Total Assets	2,008	1,791
Segment [member] | A&T [member]
Disclosure of operating segments [line items]
Total Assets	861	831
Segment [member] | AS&I [member]
Disclosure of operating segments [line items]
Total Assets	694	544
Segment [member] | Holdings & Corporate [member]
Disclosure of operating segments [line items]
Total Assets	344	304
Unallocated amounts [member]
Disclosure of operating segments [line items]
Deferred income tax assets	155	163
Cash and cash equivalents	213	164
Other financial assets	€ 26	€ 104

Other Gains _ (Losses)-Net - Su

Other Gains / (Losses)-Net - Summary of Other Gains/(Losses) Net (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Analysis of income and expense [abstract]
Realized (losses) / gains on derivatives	€ (14)	€ 15	€ (28)	€ 22
Unrealized (losses) / gains on derivatives at fair value through profit and loss - net	(14)	11	17	(43)
Unrealized exchange (losses) / gains from the remeasurement of monetary assets and liabilities - net	(1)			1
Losses on disposal	(1)	(3)	(2)	(4)
Other		1	(1)	1
Total other gains / (losses) - net	€ (30)	€ 24	€ (14)	€ (23)

Currency Gains _ (Losses) - Sum

Currency Gains / (Losses) - Summary of Currency Gains and Losses Included in Income from Operations (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Analysis of income and expense [line items]
Currency gains /(losses)	€ (2)	€ 6	€ 2	€ 6
Realized exchange (losses) / gains on foreign currency derivatives - net		(1)	1	1
Unrealized (losses) / gains on foreign currency derivatives - net	(1)	4	1	3
Exchanges (losses) / gains from the remeasurement of monetary assets and liabilities - net	(1)	3		2
Revenue [member]
Analysis of income and expense [line items]
Currency gains /(losses)	(1)	1	(2)	3
Cost of sales [member]
Analysis of income and expense [line items]
Currency gains /(losses)		2
Other (losses) / gains - net [member]
Analysis of income and expense [line items]
Currency gains /(losses)	€ (1)	€ 3	€ 4	€ 3

Finance Costs-Net - Summary of

Finance Costs-Net - Summary of Finance Costs-Net (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Analysis of income and expense [abstract]
Interest received		€ 1		€ 3
Finance income		1		3
Interest expense on borrowings	€ (30)	(30)	€ (62)	(58)
Expenses on factoring arrangements	(5)	(5)	(10)	(9)
Interest expense on lease liabilities	(4)	(1)	(7)	(2)
Realized and unrealized (losses) / gains on debt derivatives at fair value	(4)	23	5	16
Realized and unrealized exchange gains / (losses) on financing activities - net	6	(22)		(11)
Interest cost on pension and other benefits	(4)	(4)	(8)	(8)
Other finance expenses	(2)	(2)	(8)	(11)
Capitalized borrowing costs			1	2
Finance expense	(43)	(41)	(89)	(81)
Finance costs - net	€ (43)	€ (40)	€ (89)	€ (78)

Finance Costs-Net - Summary o_2

Finance Costs-Net - Summary of Finance Costs-Net (Parenthetical) (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Analysis of income and expense [line items]
Other finance expense	€ (2)	€ (2)	€ (8)	€ (11)
Capitalisation rate			6.00%	6.00%
Constellium N.V. Senior Notes [member]
Analysis of income and expense [line items]
Interest expense on debt instrument			€ 58	€ 56
Pan US ABL Facility [member]
Analysis of income and expense [line items]
Interest expense on debt instrument			€ 4	2
Constellium UACJ loan modification [member]
Analysis of income and expense [line items]
Other finance expense				€ (6)

Share of Income _ Loss Joint Ve

Share of Income / Loss Joint Ventures - Additional Information (Detail) - Constellium-Bowling Green [member] - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2019	Jan. 10, 2019
Disclosure of classes of share capital [line items]
Percentage of voting equity interests acquired		49.00%
Total percentage of voting equity interests acquired		51.00%
Remeasurement profit	€ 5

Share Of Income _ (Loss) Of J_3

Share Of Income / (Loss) Of Joint Ventures - Summary of Share of Income/ Loss of Joint Venture (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Statement [LineItems]
Revenue	€ 1,538	€ 1,474	€ 3,074	€ 2,860
Cost of sales	(1,356)	(1,300)	(2,748)	(2,549)
Selling and administrative expenses	(70)	(59)	(138)	(117)
Income from operations	69	129	149	150
Finance costs	(43)	(41)	(89)	(81)
Net income	€ 17	55	€ 41	31	€ 190
Constellium-Bowling Green [member]
Statement [LineItems]
Revenue		72		118
Cost of sales		(82)		(141)
Selling and administrative expenses		(2)		(5)
Income from operations		(12)		(28)
Finance costs		(5)		4
Net income		€ (17)		€ (24)

Share Of Income _ (Loss) Of J_4

Share Of Income / (Loss) Of Joint Ventures - Summary of Share of Income/ Loss of Joint Venture (Parenthetical) (Detail) € in Millions	Jun. 30, 2018EUR (€)
Share of profit (loss) of associates and joint ventures accounted for using equity method [abstract]
Gain related shareholders loan facilities modification	€ 12

Earnings Per Share - Earnings A

Earnings Per Share - Earnings Attributable to Equity Holders of Parent used to Calculate Basic and Diluted Earnings per share (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings per share [abstract]
Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share	€ 16	€ 55	€ 39	€ 31

Earnings Per Share - Summary of

Earnings Per Share - Summary of Number of Shares Attributable to Equity Holders (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Weighted average ordinary shares and adjusted weighted average ordinary shares [abstract]
Weighted average number of ordinary shares used to calculate basic earnings per share	136,700,491	134,562,177	136,344,030	134,517,869
Effect of other dilutive potential ordinary shares	3,620,938	4,471,455	4,005,235	4,515,005
Weighted average number of ordinary shares used to calculate diluted earnings per share	140,321,429	139,033,632	140,349,265	139,032,874

Earnings Per Share - Summary _2

Earnings Per Share - Summary of Earnings Per Share Attributable to the Equity Holders (Detail) - € / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings per share [abstract]
Basic	€ 0.12	€ 0.41	€ 0.29	€ 0.23
Diluted	€ 0.11	€ 0.39	€ 0.28	€ 0.22

Cash and Cash Equivalents - Sum

Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents [abstract]
Cash in bank and on hand	€ 213	€ 164
Total Cash and cash equivalents	€ 213	€ 164	€ 269

Cash and Cash Equivalents - Add

Cash and Cash Equivalents - Additional Information (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of cash and cash equivalents [line Items]
Cash in bank and on hand	€ 213	€ 164
Subsidiaries in capital control restrictions countries [member]
Disclosure of cash and cash equivalents [line Items]
Cash in bank and on hand	€ 21	€ 18

Trade Receivables and Other - S

Trade Receivables and Other - Summary of Trade Receivables and Other (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of trade and other receivables [line items]
Non-current trade receivables	€ 0	€ 0
Income tax receivables	27	28
Other taxes	0	0
Contract assets	30	28
Prepaid expenses		1
Other	10	7
Total Other receivables	67	64
Total Trade receivables and Other	67	64
Current trade receivables	521	481
Income tax receivables	44	43
Other taxes	26	33
Contract assets	1	2
Prepaid expenses	16	12
Other	22	16
Total Other receivables	109	106
Total Trade receivables and Other	630	587
Gross value [member]
Disclosure of trade and other receivables [line items]
Non-current trade receivables	0	0
Current trade receivables	523	483
Impairment [member]
Disclosure of trade and other receivables [line items]
Non-current trade receivables	0	0
Current trade receivables	€ (2)	€ (2)

Trade Receivables and Other -_2

Trade Receivables and Other - Summary of Contract Assets (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of disaggregation of revenue from contracts with customers [line items]
Non-current	€ 30	€ 28
Current	1	2
Unbilled Tooling Costs [member]
Disclosure of disaggregation of revenue from contracts with customers [line items]
Non-current	29	26
Other Cost [member]
Disclosure of disaggregation of revenue from contracts with customers [line items]
Non-current	1	2
Current	€ 1	€ 2

Trade Receivables and Other -_3

Trade Receivables and Other - Summary of Ageing of Total Trade Receivables - Net (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Trade receivables [line items]
Trade receivables-net	€ 521	€ 481
Current [member]
Trade receivables [line items]
Trade receivables-net	499	453
Past Due 1 to 30 Days [member]
Trade receivables [line items]
Trade receivables-net	19	23
Past Due 31 to 60 Days [member]
Trade receivables [line items]
Trade receivables-net	1	2
Past Due 61 to 90 Days [member]
Trade receivables [line items]
Trade receivables-net	1	2
Past Due Greater Than 91 Days [member]
Trade receivables [line items]
Trade receivables-net	€ 1	€ 1

Trade Receivables and Other - A

Trade Receivables and Other - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019EUR (€)	Jun. 30, 2018EUR (€)	Dec. 31, 2018EUR (€)
Disclosure of trade and other receivables [line items]
Allowance / (Reversal) of impairment		€ 100,000	€ (400,000)
Factored assets		631,000,000		€ 601,000,000
Factored assets, derecognized from Consolidated Statement of Financial Position		471,000,000		446,000,000
Factored assets, recognized in Consolidated Statement of Financial Position		160,000,000		155,000,000
Debt due factor		€ 0		€ 0
Factoring of receivables [member] | Muscle Shoals factoring facility [member]
Disclosure of trade and other receivables [line items]
Factoring maximum capacity | $	$ 375,000,000
Trade receivable factoring agreement maturity date	Jan. 24, 2020	Jan. 24, 2020
France [member] | Factoring of receivables [member]
Disclosure of trade and other receivables [line items]
Factoring maximum capacity		€ 235,000,000
Trade receivable factoring agreement maturity date	Oct. 29, 2021	Oct. 29, 2021
Germany Switzerland and Czech Republic [member] | Factoring of receivables [member]
Disclosure of trade and other receivables [line items]
Factoring maximum capacity		€ 150,000,000
Trade receivable factoring agreement maturity date	Oct. 29, 2021	Oct. 29, 2021
United States [member] | Factoring of receivables [member] | Constellium automotive [member]
Disclosure of trade and other receivables [line items]
Factoring maximum capacity | $	$ 33,000,000
Trade receivable factoring agreement maturity date	Dec. 11, 2019	Dec. 11, 2019

Trade Receivables and Other -_4

Trade Receivables and Other - Summary of Carrying Amounts of Total Trade Receivables - Net by Currency (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Trade receivables [line items]
Total Trade receivables - net	€ 521	€ 481
Euro [member]
Trade receivables [line items]
Total Trade receivables - net	230	177
U.S. Dollar [member]
Trade receivables [line items]
Total Trade receivables - net	271	284
Swiss Franc [member]
Trade receivables [line items]
Total Trade receivables - net	7	4
Other currencies [member]
Trade receivables [line items]
Total Trade receivables - net	€ 13	€ 16

Inventories - Disclosure of Inv

Inventories - Disclosure of Inventories (Detail) - EUR (€) € in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Classes of current inventories [abstract]
Finished goods	€ 186	€ 165
Work in progress	346	347
Raw materials	137	112
Stores and supplies	75	67
Inventories write down	(31)	(31)
Total Inventories	€ 713	€ 660

Property Plant and Equipment -

Property Plant and Equipment - Summary of Property Plant and Equipment (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	€ 1,666
Property, plant and equipment acquired through business combination	165
Additions	154
Disposals	(2)
Depreciation expense	(112)
Transfer during the period	(1)
Effects of changes in foreign exchange rates	9
Net balance, ending	1,981
Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	3,034
Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(1,053)
IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	102
Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,768
Land and property rights.[member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	18
Net balance, ending	18
Land and property rights.[member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	34
Land and property rights.[member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(16)
Land and property rights.[member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	18
Buildings [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	217
Property, plant and equipment acquired through business combination	40
Additions	14
Depreciation expense	(12)
Transfer during the period	4
Effects of changes in foreign exchange rates	2
Net balance, ending	347
Buildings [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	492
Buildings [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(145)
Buildings [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	82
Buildings [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	299
Machinery and equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,227
Property, plant and equipment acquired through business combination	120
Additions	40
Disposals	(2)
Depreciation expense	(95)
Transfer during the period	65
Effects of changes in foreign exchange rates	6
Net balance, ending	1,378
Machinery and equipment [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	2,236
Machinery and equipment [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(858)
Machinery and equipment [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	17
Machinery and equipment [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,244
Construction Work in Progress [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	194
Property, plant and equipment acquired through business combination	4
Additions	99
Transfer during the period	(72)
Effects of changes in foreign exchange rates	1
Net balance, ending	226
Construction Work in Progress [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	232
Construction Work in Progress [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(6)
Construction Work in Progress [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	194
Other [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	10
Property, plant and equipment acquired through business combination	1
Additions	1
Depreciation expense	(5)
Transfer during the period	2
Net balance, ending	12
Other [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	40
Other [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(28)
Other [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	3
Other [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	€ 13

Property Plant and Equipment _2

Property Plant and Equipment - Summary of Property Plant and Equipment Right of Use Assets (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	€ 1,666
Additions	154
Disposals	(2)
Depreciation expense	(112)
Effects of changes in foreign exchange rates	9
Net balance, ending	1,981
IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	102
Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,768
Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	3,034
Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(1,053)
Right-of-use assets [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	77
Additions	27
Disposals	0
Depreciation expense	(14)
Effects of changes in foreign exchange rates	1
Net balance, ending	193
Right-of-use assets [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	102
Right-of-use assets [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	179
Right-of-use assets [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	240
Right-of-use assets [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(47)
Buildings [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	217
Additions	14
Depreciation expense	(12)
Effects of changes in foreign exchange rates	2
Net balance, ending	347
Buildings [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	82
Buildings [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	299
Buildings [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	492
Buildings [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(145)
Buildings [member] | Right-of-use assets [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	24
Additions	13
Disposals	0
Depreciation expense	(5)
Effects of changes in foreign exchange rates	1
Net balance, ending	115
Buildings [member] | Right-of-use assets [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	82
Buildings [member] | Right-of-use assets [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	106
Buildings [member] | Right-of-use assets [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	127
Buildings [member] | Right-of-use assets [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(12)
Machinery and equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,227
Additions	40
Disposals	(2)
Depreciation expense	(95)
Effects of changes in foreign exchange rates	6
Net balance, ending	1,378
Machinery and equipment [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	17
Machinery and equipment [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	1,244
Machinery and equipment [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	2,236
Machinery and equipment [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(858)
Machinery and equipment [member] | Right-of-use assets [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	53
Additions	13
Disposals	0
Depreciation expense	(8)
Net balance, ending	75
Machinery and equipment [member] | Right-of-use assets [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	17
Machinery and equipment [member] | Right-of-use assets [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	70
Machinery and equipment [member] | Right-of-use assets [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	109
Machinery and equipment [member] | Right-of-use assets [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(34)
Other [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	10
Additions	1
Depreciation expense	(5)
Net balance, ending	12
Other [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	3
Other [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	13
Other [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	40
Other [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	(28)
Other [member] | Right-of-use assets [member]
Disclosure of detailed information about property, plant and equipment [line items]
Additions	1
Disposals	0
Depreciation expense	(1)
Net balance, ending	3
Other [member] | Right-of-use assets [member] | IFRS 16 [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	3
Other [member] | Right-of-use assets [member] | Restated [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, beginning	3
Other [member] | Right-of-use assets [member] | Gross value [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	4
Other [member] | Right-of-use assets [member] | Accumulated depreciation [member]
Disclosure of detailed information about property, plant and equipment [line items]
Net balance, ending	€ (1)

Property Plant and Equipment _3

Property Plant and Equipment - Summary of Property Plant and Equipment Right of Use Assets (Parenthetical) (Detail) - IFRS 16 [member] € in Millions	Jan. 01, 2019EUR (€)
Finance lease [member]
Disclosure of detailed information about property, plant and equipment [line items]
Right-of-use asset	€ 77
Operating lease [member]
Disclosure of detailed information about property, plant and equipment [line items]
Right-of-use asset	€ 102

Property Plant and Equipment _4

Property Plant and Equipment - Additional Information (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)
Disclosure of detailed information about property, plant and equipment [abstract]
Operating lease expenses	€ 7

Intangible Assets (Including _3

Intangible Assets (Including Goodwill) - Disclosure of Changes in Intangible Assets and Goodwill (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill, beginning balance	€ 422
Goodwill acquired through business combination	22
Effects of changes in foreign exchange rates	3
Goodwill, ending balance	447
Intangible assets (excluding goodwill), beginning balance	70
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), additions	1
Intangible assets (excluding goodwill), amortization expense	(5)
Intangible assets (excluding goodwill), transfer during the period	1
Intangible assets (excluding goodwill), effects of changes in foreign exchange rates	1
Intangible assets (excluding goodwill), ending balance	68
Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill, ending balance	447
Intangible assets (excluding goodwill), ending balance	208
Accumulated amortization and impairment [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	(140)
Technology [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), beginning balance	22
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), amortization expense	(2)
Intangible assets (excluding goodwill), effects of changes in foreign exchange rates	1
Intangible assets (excluding goodwill), ending balance	21
Technology [member] | Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	85
Technology [member] | Accumulated amortization and impairment [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	(64)
Computer software [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), beginning balance	18
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), amortization expense	(3)
Intangible assets (excluding goodwill), transfer during the period	1
Intangible assets (excluding goodwill), ending balance	16
Computer software [member] | Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	67
Computer software [member] | Accumulated amortization and impairment [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	(51)
Customer relationships [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), beginning balance	15
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), ending balance	15
Customer relationships [member] | Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	40
Customer relationships [member] | Accumulated amortization and impairment [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	(25)
Work in progress [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), beginning balance	13
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), additions	1
Intangible assets (excluding goodwill), ending balance	14
Work in progress [member] | Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	14
Other intangible assets [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), beginning balance	2
Intangible assets acquired through business combination	0
Intangible assets (excluding goodwill), ending balance	2
Other intangible assets [member] | Gross value [member]
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Intangible assets (excluding goodwill), ending balance	€ 2

Trade Payables and Other - Deta

Trade Payables and Other - Detailed Information about Trade and Other Payables (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Trade and other payables [abstract]
Trade payables	€ 0	€ 0
Fixed asset payables	0	0
Employees' entitlements	0	0
Taxes payable other than income tax	0	0
Contract liabilities	11	9
Other payables	17	18
Total Other	28	27
Total Trade payables and Other (non-current)	28	27
Trade payables	838	685
Fixed asset payables	29	30
Employees' entitlements	162	160
Taxes payable other than income tax	25	16
Contract liabilities	59	68
Other payables	7	9
Total Other	282	283
Total Trade payables and Other (current)	€ 1,120	€ 968

Trade Payables and Other - De_2

Trade Payables and Other - Detailed information of contract liabilities (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	€ 11	€ 9
Current	59	68
Deferred Tooling Revenue [member]
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	5
Advance Payment From Customers [member]
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	4	7
Current	6	9
Unrecognized Variable Consideration [member]
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	2	2
Current	52	57
Prepayment [member]
Disclosure of disaggregation of contract liabilities with customers [line items]
Current	€ 1	€ 2

Trade Payables and Other - Addi

Trade Payables and Other - Additional Information (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)
Receivables from contracts with customers [abstract]
Revenue recognized related to contract liabilities	€ 25
Deferred revenue related to contract liabilities	€ 30

Borrowings - Summary of Borrowi

Borrowings - Summary of Borrowings (Detail)	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019EUR (€)	Jan. 01, 2019EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)
Disclosure of detailed information about borrowings [line items]
Nominal Value		€ 2,373,000,000
Arrangement fees		(29,000,000)
Accrued interest		34,000,000
Borrowings		2,378,000,000	€ 2,253,000,000	€ 2,151,000,000	€ 2,127,000,000
Non-current		2,216,000,000		2,094,000,000
Current		162,000,000		57,000,000
Constellium SE senior unsecured notes (Issued May 2014, due 2024) [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value	$ 400,000,000	€ 352,000,000
Nominal rate	5.75%
Effective rate	6.26%	6.26%
Arrangement fees		€ (3,000,000)
Accrued interest		2,000,000
Borrowings		351,000,000		348,000,000
Constellium SE senior unsecured notes (Issued May 2014, due 2021) [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value		€ 300,000,000
Nominal rate	4.63%
Effective rate	5.16%	5.16%
Arrangement fees		€ (2,000,000)
Accrued interest		2,000,000
Borrowings		300,000,000		300,000,000
Constellium Se senior unsecured notes (Issued February 2017, due 2025) [Member]
Disclosure of detailed information about borrowings [line items]
Nominal Value	$ 650,000,000	€ 571,000,000
Nominal rate	6.63%
Effective rate	7.13%	7.13%
Arrangement fees		€ (11,000,000)
Accrued interest		13,000,000
Borrowings		573,000,000		568,000,000
Constellium SE senior unsecured notes (Issued November 2017, due 2026) [Member]
Disclosure of detailed information about borrowings [line items]
Nominal Value	$ 500,000,000	€ 439,000,000
Nominal rate	5.88%
Effective rate	6.26%	6.26%
Arrangement fees		€ (7,000,000)
Accrued interest		10,000,000
Borrowings		442,000,000		440,000,000
Constellium SE senior unsecured notes (Issued November 2017, due 2026) [Member]
Disclosure of detailed information about borrowings [line items]
Nominal Value		€ 400,000,000
Nominal rate	4.25%
Effective rate	4.57%	4.57%
Arrangement fees		€ (6,000,000)
Accrued interest		6,000,000
Borrowings		400,000,000		399,000,000
Lease liabilities [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value		187,000,000
Borrowings		187,000,000		73,000,000
Other loans [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value		31,000,000
Accrued interest		1,000,000
Borrowings		32,000,000		€ 23,000,000
Pan US ABL facility (due 2022) [member]
Disclosure of detailed information about borrowings [line items]
Nominal rate	Floating
Nominal Value	$ 106,000,000	€ 93,000,000
Effective rate	4.43%	4.43%
Borrowings		€ 93,000,000
Secured inventory based facility (due 2019) [member]
Disclosure of detailed information about borrowings [line items]
Nominal rate	Floating
Unsecured revolving credit facilities (due 2021) [member]
Disclosure of detailed information about borrowings [line items]
Nominal rate	Floating

Borrowings - Summary of Borro_2

Borrowings - Summary of Borrowings (Parenthetical) (Detail) $ in Millions	Mar. 15, 2019	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2019EUR (€)	May 10, 2019USD ($)	Feb. 20, 2019USD ($)	Jan. 01, 2019EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)
Disclosure of detailed information about borrowings [line items]
Nominal Value				€ 2,373,000,000
Borrowings				2,378,000,000			€ 2,253,000,000	€ 2,151,000,000	€ 2,127,000,000
Pan US ABL facility (due 2022) [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value			$ 106	93,000,000
Borrowings				93,000,000
Pan US ABL facility (due 2022) [member] | Constellium-Bowling Green [member]
Disclosure of detailed information about borrowings [line items]
Nominal Value | $					$ 400	$ 350
Secured inventory based facility (due 2019) [member]
Disclosure of detailed information about borrowings [line items]
Secured Inventory Based Facility maturity	2021-12
BPI unsecured revolving credit facilities [member]
Disclosure of detailed information about borrowings [line items]
Borrowing capacity		€ 7,000,000
Third Party Funding Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings				€ 11,000,000

Borrowings - Summary of Reconci

Borrowings - Summary of Reconciliation of Movement in Net Borrowings Explanatory (Detail) - EUR (€) € in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure of detailed information about borrowings [abstract]
Beginning Balance	€ 2,151	€ 2,127	€ 2,127
IFRS 16 application	102
At January 1	2,253
Proceeds / (Repayments) from Revolving Credit Facilities and other loans	76		(68)
Payment of lease liabilities	(70)	€ (7)	(15)
Borrowings assumed through business combination	75
New leases and other loans	33		28
Movement in interests accrued	1		12
Deferred arrangement fees	2		2
Effects of changes in foreign exchange rates	8		65
Ending Balance	€ 2,378		€ 2,151

Borrowings - Summary of Composi

Borrowings - Summary of Composition of Carrying Amounts of Total Borrowings (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about borrowings [line items]
Total borrowings	€ 2,378	€ 2,253	€ 2,151	€ 2,127
U.S. Dollar [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	1,541		1,408
Euro [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	811		726
Other currencies [member]
Disclosure of detailed information about borrowings [line items]
Total borrowings	€ 26		€ 17

Borrowings - Additional Informa

Borrowings - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019
Pan US ABL facility (due 2022) [member]
Disclosure of detailed information about borrowings [line items]
Debt covenant, Percentage of aggregate revolving loan commitments	10.00%

Financial Instruments - Summary

Financial Instruments - Summary of Financial Assets and Liabilities by Categories (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items]
Cash and cash equivalents	€ 213		€ 164	€ 269
Trade receivables	521		481
Other financial assets	26		104
Total financial assets	760		749
Trade payables and fixed assets payables	867		715
Borrowings	2,378	€ 2,253	2,151	€ 2,127
Other financial liabilities	69		89
Total financial liabilities	3,314		2,955
At amortized cost [member]
Disclosure of detailed information about financial instruments [line items]
Trade payables and fixed assets payables	867		715
Borrowings	2,378		2,151
Total financial liabilities	3,245		2,866
At fair value through Profit and loss [member]
Disclosure of detailed information about financial instruments [line items]
Other financial liabilities	58		79
Total financial liabilities	58		79
At fair value through OCI [member]
Disclosure of detailed information about financial instruments [line items]
Other financial liabilities	11		10
Total financial liabilities	11		10
At amortized cost [member]
Disclosure of detailed information about financial instruments [line items]
Cash and cash equivalents	213		164
Other financial assets			74
Total financial assets	213		238
At fair value through Profit and loss [member]
Disclosure of detailed information about financial instruments [line items]
Other financial assets	26		30
Total financial assets	26		30
At fair value through OCI [member]
Disclosure of detailed information about financial instruments [line items]
Trade receivables	521		481
Total financial assets	€ 521		€ 481

Financial Instruments - Summa_2

Financial Instruments - Summary of Other Financial Assets and Other Financial Liabilities Positions (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Non-current derivative financial assets	€ 7	€ 7
Current derivative financial assets	19	23
Derivatives assets	26	30
Non-current loans		67
Current loans		2
Loans		69
Other non-current financial assets	7	74
Other current financial assets	19	30
Other financial assets	26	104
Other non-current financial liabilities	25	29
Other current financial liabilities	44	60
Other financial liabilities	69	89
Non-current derivative financial liabilities	25	29
Current derivative financial liabilities	44	60
Derivatives Liabilities	69	89
Aluminium and premium future contract [member]
Disclosure of detailed information about financial instruments [line items]
Non-current derivative financial assets	2	2
Current derivative financial assets	4	7
Derivatives assets	6	9
Non-current derivative financial liabilities	5	6
Current derivative financial liabilities	22	38
Derivatives Liabilities	27	44
Other future contract [member]
Disclosure of detailed information about financial instruments [line items]
Non-current derivative financial liabilities	3	5
Current derivative financial liabilities	3	3
Derivatives Liabilities	6	8
Currency commercial contracts [member]
Disclosure of detailed information about financial instruments [line items]
Non-current derivative financial assets	5	3
Current derivative financial assets	12	12
Derivatives assets	17	15
Non-current derivative financial liabilities	10	7
Current derivative financial liabilities	14	12
Derivatives Liabilities	24	19
Currency net debt derivatives [member]
Disclosure of detailed information about financial instruments [line items]
Non-current derivative financial assets		2
Current derivative financial assets	3	4
Derivatives assets	3	6
Non-current derivative financial liabilities	7	11
Current derivative financial liabilities	5	3
Derivatives Liabilities	€ 12	14
Margin call [member]
Disclosure of detailed information about financial instruments [line items]
Current derivative financial assets		5
Derivatives assets		5
Net investment hedge [member]
Disclosure of detailed information about financial instruments [line items]
Current derivative financial liabilities		4
Derivatives Liabilities		€ 4

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - Fair value [member] € in Millions	Jun. 30, 2019EUR (€)
Constellium N.V. senior unsecured notes (Issued May 2014) [member]
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	102.00%
Senior Notes issued	€ 664
Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025) [member]
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	104.00%
Senior Notes issued	€ 596
Constellium N.V. EUR and USD Senior Unsecured Notes (Issued November 2017, due 2026) [member]
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	103.00%
Senior Notes issued	€ 866

Financial Instruments - Summa_3

Financial Instruments - Summary of Derivatives Measured at Fair Value (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of financial instruments measured at fair value [line items]
Other financial assets-derivatives	€ 26	€ 30
Other financial liabilities-derivatives	69	89
Level 1 of fair value hierarchy [member]
Disclosure of financial instruments measured at fair value [line items]
Other financial assets-derivatives	5	9
Other financial liabilities-derivatives	32	50
Level 2 of fair value hierarchy [member]
Disclosure of financial instruments measured at fair value [line items]
Other financial assets-derivatives	21	21
Other financial liabilities-derivatives	€ 37	€ 39

Financial Risk Management - Add

Financial Risk Management - Additional Information (Detail) € in Millions, SFr in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2019EUR (€)	Jun. 30, 2019CHF (SFr)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)
Disclosure of liquidity risk [line items]
Liquidity value			€ 588
Cash and cash equivalents			213			€ 164	€ 269
Undrawn facilities			375
Revolving credit facilities outstanding			314
Forward contract [member]
Disclosure of liquidity risk [line items]
Total nominal amount forward contracts | SFr				SFr 174
Realized gain / loss of the net investment hedge	€ (2.8)
Derivative classified as cash flow hedge [member]
Disclosure of liquidity risk [line items]
Nominal amount hedging instrument | $		$ 296			$ 369
Pan US ABL facility (due 2022) [member]
Disclosure of liquidity risk [line items]
Borrowing base | $		$ 374
French inventory facility [member]
Disclosure of liquidity risk [line items]
Borrowing base			€ 78
Top of range [member] | Derivative classified as cash flow hedge [member]
Disclosure of liquidity risk [line items]
Maturity period	2022
Bottom of range [member] | Derivative classified as cash flow hedge [member]
Disclosure of liquidity risk [line items]
Maturity period	2019

Financial Risk Management - Sum

Financial Risk Management - Summary of Effect of Foreign Currency Derivatives Impacts and Commercial Transactions Exposures (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized (losses) / gains on foreign currency derivatives - net		€ (1)	€ 1	€ 1
Unrealized (losses) / gains on foreign currency derivatives - net	€ (1)	4	1	3
Derivatives that do not qualify for hedge accounting [member] | Other gains (losses) [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized (losses) / gains on foreign currency derivatives - net	2	(1)	4	(2)
Unrealized (losses) / gains on foreign currency derivatives - net	(1)	5	1	4
Derivatives that qualify for hedge accounting [member] | Other gains (losses) [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized (losses) / gains on foreign currency derivatives - net	(1)	(2)	(1)	(1)
Derivatives that qualify for hedge accounting [member] | Revenue [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized (losses) / gains on foreign currency derivatives - net	(1)	2	(2)	4
Unrealized (losses) / gains on foreign currency derivatives - net		(1)		(1)
Derivatives that qualify for hedge accounting [member] | Other comprehensive income (loss) [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Unrealized (losses) / gains on foreign currency derivatives - net	1	(22)	(7)	(11)
Gains / (Losses) reclassified from cash flow hedge reserve to Consolidated Income Statement	€ 1	€ (1)	€ 2	€ (3)

Pensions and Other Post-emplo_3

Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Detail)	Jun. 30, 2019	Dec. 31, 2018
Switzerland [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.30%	0.80%
United States [member] | Salaried pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.70%	4.45%
France [member] | Retirements [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.85%	1.65%
France [member] | Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.65%	1.35%
Germany [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.90%	1.70%
Bottom of range [member] | United States [member] | Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.60%	4.40%
Bottom of range [member] | United States [member] | Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.65%	4.40%
Bottom of range [member] | United States [member] | Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.40%	4.25%
Top of range [member] | United States [member] | Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.70%	4.45%
Top of range [member] | United States [member] | Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.85%	4.55%
Top of range [member] | United States [member] | Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.65%	4.40%

Pensions and Other Post-emplo_4

Pensions and Other Post-employment Benefit Obligations - Summary of Amounts Recognized in the Consolidated Statement of Financial Position (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of net defined benefit liability (asset) [line items]
Present value of funded obligation	€ 745	€ 674
Fair value of plan assets	(419)	(380)
Deficit of funded plans	326	294
Present value of unfunded obligation	346	316
Net liability arising from defined benefit obligation	672	610
Pension benefits [member]
Disclosure of net defined benefit liability (asset) [line items]
Present value of funded obligation	745	674
Fair value of plan assets	(419)	(380)
Deficit of funded plans	326	294
Present value of unfunded obligation	131	115
Net liability arising from defined benefit obligation	457	409
Other benefits [member]
Disclosure of net defined benefit liability (asset) [line items]
Present value of unfunded obligation	215	201
Net liability arising from defined benefit obligation	€ 215	€ 201

Pensions and Other Post-Emplo_5

Pensions and Other Post-Employment Benefit Obligations - Summary of Amounts recognized in the Unaudited Interim Consolidated Income Statement (Detail) - Consolidated Income Statement [member] - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement [LineItems]
Current service cost	€ (6)	€ (5)	€ (12)	€ (11)
Net interest	(4)	(4)	(8)	(8)
Immediate recognition of gains / (losses) arising over the period	(2)		(2)
Administrative expenses		(1)	(1)	(1)
Total	(12)	(10)	(23)	(20)
Pension Benefits [member]
Statement [LineItems]
Current service cost	(5)	(3)	(9)	(8)
Net interest	(2)	(2)	(4)	(4)
Administrative expenses		(1)	(1)	(1)
Total	(7)	(6)	(14)	(13)
Other benefits [member]
Statement [LineItems]
Current service cost	(1)	(2)	(3)	(3)
Net interest	(2)	(2)	(4)	(4)
Immediate recognition of gains / (losses) arising over the period	(2)		(2)
Total	€ (5)	€ (4)	€ (9)	€ (7)

Pensions and Other Post-emplo_6

Pensions and Other Post-employment Benefit Obligations - Details of Movement in Net Defined Benefit Obligations (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			€ 610
Closing balance	€ 672		672
Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	6	€ 5	12	€ 11
Interest cost / (income)			8
Immediate recognition of gains / (losses) arising over the period	2		2
Administration expenses		1	1	1
Statement of Comprehensive Income (Loss) [member]
Disclosure of net defined benefit liability (asset) [line items]
- actual return less interest on plan assets			(32)
- changes in financial assumptions			93
- changes in demographic assumptions			0
- experience losses			(1)
Effects of changes in foreign exchange rates			3
Consolidated Statement of Cash Flows [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits paid			(12)
Contributions by the Group			(12)
Other benefits [member] | Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	1	€ 2	3	€ 3
Immediate recognition of gains / (losses) arising over the period	2		2
Defined benefit obligations [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			990
Closing balance	1,091		1,091
Defined benefit obligations [member] | Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			12
Interest cost / (income)			13
Immediate recognition of gains / (losses) arising over the period			2
Defined benefit obligations [member] | Statement of Comprehensive Income (Loss) [member]
Disclosure of net defined benefit liability (asset) [line items]
- changes in financial assumptions			93
- changes in demographic assumptions			0
- experience losses			(1)
Effects of changes in foreign exchange rates			7
Defined benefit obligations [member] | Consolidated Statement of Cash Flows [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits paid			(27)
Contributions by the plan participants			2
Defined benefit obligations [member] | Pension benefits [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			789
Closing balance	876		876
Defined benefit obligations [member] | Pension benefits [member] | Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			9
Interest cost / (income)			9
Defined benefit obligations [member] | Pension benefits [member] | Statement of Comprehensive Income (Loss) [member]
Disclosure of net defined benefit liability (asset) [line items]
- changes in financial assumptions			77
- changes in demographic assumptions			0
Effects of changes in foreign exchange rates			6
Defined benefit obligations [member] | Pension benefits [member] | Consolidated Statement of Cash Flows [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits paid			(16)
Contributions by the plan participants			2
Defined benefit obligations [member] | Other benefits [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			201
Closing balance	215		215
Defined benefit obligations [member] | Other benefits [member] | Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			3
Interest cost / (income)			4
Immediate recognition of gains / (losses) arising over the period			2
Defined benefit obligations [member] | Other benefits [member] | Statement of Comprehensive Income (Loss) [member]
Disclosure of net defined benefit liability (asset) [line items]
- changes in financial assumptions			16
- changes in demographic assumptions			0
- experience losses			(1)
Effects of changes in foreign exchange rates			1
Defined benefit obligations [member] | Other benefits [member] | Consolidated Statement of Cash Flows [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits paid			(11)
Plan Assets [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			(380)
Closing balance	€ (419)		(419)
Plan Assets [member] | Consolidated Income Statement [member]
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			0
Interest cost / (income)			(5)
Immediate recognition of gains / (losses) arising over the period			0
Administration expenses			1
Plan Assets [member] | Statement of Comprehensive Income (Loss) [member]
Disclosure of net defined benefit liability (asset) [line items]
- actual return less interest on plan assets			(32)
- changes in demographic assumptions			0
Effects of changes in foreign exchange rates			(4)
Plan Assets [member] | Consolidated Statement of Cash Flows [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits paid			15
Contributions by the Group			(12)
Contributions by the plan participants			€ (2)

Pensions and Other Post-emplo_7

Pensions and Other Post-employment Benefit Obligations - Details of Net Defined Benefit Obligations by Country (Detail) - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	€ 1,091	€ 990
Plan assets	(419)	(380)
Net defined benefit liability	672	610
France [member]
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	169	151
Plan assets	(3)	(3)
Net defined benefit liability	166	148
Germany [member]
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	148	136
Plan assets	(1)	(1)
Net defined benefit liability	147	135
Switzerland [member]
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	280	251
Plan assets	(194)	(178)
Net defined benefit liability	86	73
United States [member]
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	493	451
Plan assets	(221)	(198)
Net defined benefit liability	272	253
Other countries [member]
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	1	1
Net defined benefit liability	€ 1	€ 1

Provisions - Summary of Changes

Provisions - Summary of Changes in Provisions (Detail) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure of other provisions [line items]
Beginning balance	€ 140
IFRIC 23 application	(20)
Allowance	1
Amounts used	(4)
Unused amounts reversed	(3)
Unwinding of discounts	3
Effects of changes in foreign exchange rates	0
Ending balance	117
Current	22	€ 46
Non-Current	95	€ 94
Close down and environmental remediation costs [member]
Disclosure of other provisions [line items]
Beginning balance	83
Unwinding of discounts	3
Effects of changes in foreign exchange rates	0
Ending balance	86
Current	5
Non-Current	81
Restructuring costs [member]
Disclosure of other provisions [line items]
Beginning balance	3
Effects of changes in foreign exchange rates	0
Ending balance	3
Current	2
Non-Current	1
Legal claims and other costs [member]
Disclosure of other provisions [line items]
Beginning balance	54
IFRIC 23 application	(20)
Allowance	1
Amounts used	(4)
Unused amounts reversed	(3)
Effects of changes in foreign exchange rates	0
Ending balance	28
Current	15
Non-Current	€ 13

Provisions - Summary of Legal C

Provisions - Summary of Legal Claims and Other Costs (Detail) - Legal claims and other costs [member] - EUR (€) € in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of other provisions [line items]
Litigation	€ 19	€ 45
Disease claims	4	4
Other	5	5
Total Provisions for legal claims and other costs	€ 28	€ 54

Provisions - Summary of Legal_2

Provisions - Summary of Legal Claims and Other Costs (Parenthetical) (Detail) € in Millions	Jun. 30, 2019EUR (€)
Disclosure of contingent liabilities [abstract]
Reclassification of contract liabilities	€ 20

Non Cash Investing & Financin_2

Non Cash Investing & Financing Transactions - Additional Information (Detail) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Non Cash Investing And Financing Transactions [abstract]
Property, plant and equipment acquired by finance lease	€ 33	€ 1
Fair value of PSU and RSUs vested	€ 4	€ 3

Share Capital - Additional Info

Share Capital - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019EUR (€)Voting_Rights€ / sharesshares
Disclosure of classes of share capital [abstract]
Authorized share capital | €	€ 8,000,000
Number of share authorized | shares	400,000,000
Nominal value of per shares | € / shares	€ 0.02
Shares, number of voting rights | Voting_Rights	1

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)shares
Disclosure of classes of share capital [line items]
Beginning balance | shares	135,999,394
New shares issued | shares	817,627
Ending balance | shares	136,817,021
Beginning balance	€ (114)
Ending balance	(113)
Share capital [member]
Disclosure of classes of share capital [line items]
Beginning balance	3
New shares issued	0
Ending balance	3
Share premium [member]
Disclosure of classes of share capital [line items]
Beginning balance	420
New shares issued	0
Ending balance	€ 420

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Share Based Payment Plans [line items]
Total expense related to the potential ordinary shares	€ 7	€ 6
Performance share units (PSUs) [member]
Share Based Payment Plans [line items]
Share based compensation, vesting period	3 years
Percentage of vesting multiplier	100.00%
PSUs granted in 2015 and 2016 [member] | Bottom of range [member]
Share Based Payment Plans [line items]
Percentage of vesting multiplier	0.00%
PSUs granted in 2015 and 2016 [member] | Top of range [member]
Share Based Payment Plans [line items]
Percentage of vesting multiplier	200.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Performance-Based RSU (Detail) - 2019 performance shares [member]	6 Months Ended
	Jun. 30, 2019EUR (€)€ / shares
Disclosure of Input of Model Used for Performance-Based RSU [Line Items]
Fair value at grant date (in Euros) | € / shares	€ 10.44
Share price at grant date (in Euros) | €	€ 7.10
Dividend yield	0.00%
Expected volatility	52.00%
Risk-free interest rate (U.S. government bond yield)	2.29%
Model used	Monte Carlo

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Movements in Shares (Detail)	6 Months Ended
	Jun. 30, 2019shares
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance	4,455,601
Potential Shares, Granted	1,974,638
Potential Shares, Over performance	21,802
Potential Shares, Vested	(856,224)
Potential Shares, Forfeited	(99,543)
Potential Shares, Ending balance	5,496,274
Performance-Based RSU [member]
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance	3,085,164
Potential Shares, Granted	1,028,342
Potential Shares, Over performance	21,802
Potential Shares, Vested	(807,665)
Potential Shares, Forfeited	(78,806)
Potential Shares, Ending balance	3,248,837
Restricted Stock Units [member]
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance	1,312,524
Potential Shares, Granted	899,926
Potential Shares, Vested	(6,000)
Potential Shares, Forfeited	(20,737)
Potential Shares, Ending balance	2,185,713
Equity Awards Plans [member]
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance	57,913
Potential Shares, Granted	46,370
Potential Shares, Vested	(42,559)
Potential Shares, Ending balance	61,724

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Movements in Shares (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2019shares
Disclosure of movement of potential shares [line items]
Performance based shares forfeited upon departure of certain beneficiaries	78,806
Performance based shares forfeited upon non-fulfilment of performance conditions	0
Performance share units (PSUs) [member]
Disclosure of movement of potential shares [line items]
Percentage of vesting multiplier	100.00%

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - EUR (€)	Jul. 09, 2019	Jun. 30, 2019
Statement [LineItems]
Debt instrument face amount		€ 2,373,000,000
Constellium SE senior unsecured notes (Issued May 2014, due 2021) [member]
Statement [LineItems]
Debt instrument face amount		€ 300,000,000
Interest rate on debt		5.16%
Partial Redemption [member] | Constellium SE senior unsecured notes (Issued May 2014, due 2021) [member]
Statement [LineItems]
Debt instrument face amount	€ 100,000,000
Interest rate on debt	4.625%
Debt redemption price	100.00%