Constellium SE (CSTM) 6-K 23 Jul 20 2020 Q2 Index to Unaudited Condensed Interim Consolidated Financial Statements Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2020
Document and entity information [abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Registrant Name	Constellium SE
Entity Central Index Key	0001563411
Current Fiscal Year End Date	--12-31

Document and Entity Informati_2

Document and Entity Information Document and Entity Information	6 Months Ended
	Jun. 30, 2020
Document and entity information [abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Profit or loss [abstract]
Revenue	€ 1,031	€ 1,538	€ 2,468	€ 3,074
Cost of sales	(962)	(1,356)	(2,246)	(2,748)
Gross profit	69	182	222	326
Selling and administrative expenses	(57)	(70)	(123)	(138)
Research and development expenses	(7)	(12)	(20)	(24)
Restructuring costs	(11)	(1)	(11)	(1)
Other gains / (losses) - net	5	(30)	(63)	(14)
(Loss) / income from operations	(1)	69	5	149
Finance costs - net	(42)	(43)	(87)	(89)
Share of income of joint-ventures	0	0	0	5
(Loss) / income before income tax	(43)	26	(82)	65
Income tax benefit / (expense)	11	(9)	19	(24)
Net (loss) / income	(32)	17	(63)	41
(Loss) / income attributable to:
Equity holders of Constellium	(33)	16	(64)	39
Non-controlling interests	1	1	1	2
Net (loss) / income	€ (32)	€ 17	€ (63)	€ 41
Earnings per share attributable to the equity holders of Constellium
Basic (in EUR per share)	€ (0.24)	€ 0.12	€ (0.46)	€ 0.29
Diluted (in EUR per share)	€ (0.24)	€ 0.11	€ (0.46)	€ 0.28

UNAUDITED INTERIM CONSOLIDATE_2

UNAUDITED INTERIM CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME / (LOSS) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of comprehensive income [abstract]
Net (loss) / income	€ (32)	€ 17	€ (63)	€ 41
Items that will not be reclassified subsequently to the Unaudited Interim Consolidated Income Statement
Remeasurement on post-employment benefit obligations	(35)	(34)	(41)	(62)
Income tax on remeasurement on post-employment benefit obligations	10	8	9	15
Items that may be reclassified subsequently to the Unaudited Interim Consolidated Income Statement
Cash flow hedges	5	2	0	(5)
Net investment hedges	0	5	0	4
Income tax on hedges	(2)	0	0	2
Currency translation differences	(2)	(6)	(2)	(1)
Other comprehensive loss	(24)	(25)	(34)	(47)
Total comprehensive loss	(56)	(8)	(97)	(6)
Attributable to:
Equity holders of Constellium	(57)	(9)	(98)	(8)
Non-controlling interests	1	1	1	2
Total comprehensive loss	€ (56)	€ (8)	€ (97)	€ (6)

UNAUDITED INTERIM CONSOLIDATE_3

UNAUDITED INTERIM CONSOLIDATED STATEMENT OF FINANCIAL POSITION - EUR (€)	Jun. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	€ 378,000,000	€ 184,000,000
Trade receivables and other	451,000,000	474,000,000
Inventories	635,000,000	670,000,000
Other financial assets	22,000,000	22,000,000
Total current assets	1,486,000,000	1,350,000,000
Non-current assets
Property, plant and equipment	2,031,000,000	2,056,000,000
Goodwill	456,000,000	455,000,000
Intangible assets	68,000,000	70,000,000
Investments accounted for under the equity method	1,000,000	1,000,000
Deferred income tax assets	222,000,000	185,000,000
Trade receivables and other	74,000,000	60,000,000
Other financial assets	9,000,000	7,000,000
Total non-current assets	2,861,000,000	2,834,000,000
Total Assets	4,347,000,000	4,184,000,000
Current liabilities
Trade payables and other	1,003,000,000	999,000,000
Borrowings	102,000,000	201,000,000
Other financial liabilities	45,000,000	35,000,000
Income tax payable	20,000,000	14,000,000
Provisions	29,000,000	23,000,000
Total current liabilities	1,199,000,000	1,272,000,000
Non-current liabilities
Trade payables and other	19,000,000	21,000,000
Borrowings	2,434,000,000	2,160,000,000
Other financial liabilities	30,000,000	23,000,000
Pension and other post-employment benefit obligations	715,000,000	670,000,000
Provisions	99,000,000	99,000,000
Deferred income tax liabilities	25,000,000	24,000,000
Total non-current liabilities	3,322,000,000	2,997,000,000
Total Liabilities	4,521,000,000	4,269,000,000
Equity
Share capital	2,758,440.64	3,000,000
Share premium	420,000,000	420,000,000
Retained deficit and other reserves	(609,000,000)	(519,000,000)
Equity attributable to equity holders of Constellium	(186,000,000)	(96,000,000)
Non controlling interests	12,000,000	11,000,000
Total Equity	(174,000,000)	(85,000,000)
Total Equity and Liabilities	€ 4,347,000,000	€ 4,184,000,000

UNAUDITED INTERIM CONSOLIDATE_4

UNAUDITED INTERIM CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - EUR (€) € in Millions	Total	Share capital	Share premium	Re-measurement	Cash flow hedges	Foreign currency translation reserve	Other reserves	Retained losses	Total Equity holders of Constellium	Non-controlling interests
Beginning balance at Dec. 31, 2018	€ (114)	€ 3	€ 420	€ (129)	€ (8)	€ 3	€ 37	€ (448)	€ (122)	€ 8
Net (loss) / income	41							39	39	2
Other comprehensive loss	(47)			(47)	1	(1)			(47)
Total comprehensive loss	(6)			(47)	1	(1)		39	(8)	2
Share-based compensation	7						7		7
Transactions with non-controlling interests	0									0
Ending balance at Jun. 30, 2019	(113)	3	420	(176)	(7)	2	44	(409)	(123)	10
Beginning balance at Dec. 31, 2018	(114)	3	420	(129)	(8)	3	37	(448)	(122)	8
Net (loss) / income	64							59	59	5
Other comprehensive loss	(49)			(48)	(2)	1			(49)	0
Total comprehensive loss	15			(48)	(2)	1		59	10	5
Share-based compensation	16						16		16
Transactions with non-controlling interests	(2)									(2)
Ending balance at Dec. 31, 2019	(85)	3	420	(177)	(10)	4	53	(389)	(96)	11
Net (loss) / income	(63)							(64)	(64)	1
Other comprehensive loss	(34)			(32)	0	(2)			(34)
Total comprehensive loss	(97)			(32)	0	(2)		(64)	(98)	1
Share issuance		0	0
Share-based compensation	8						8		8
Transactions with non-controlling interests	0									0
Ending balance at Jun. 30, 2020	€ (174)	€ 3	€ 420	€ (209)	€ (10)	€ 2	€ 61	€ (453)	€ (186)	€ 12

UNAUDITED INTERIM CONSOLIDATE_5

UNAUDITED INTERIM CONSOLIDATED STATEMENT OF CASH FLOWS - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Statement of cash flows [abstract]
Net (loss) / income	€ (63)	€ 41
Adjustments
Depreciation, amortization and impairment	137	117
Finance costs - net	87	89
Tax (benefit) / expense	(19)	24
Share of income of joint-ventures	0	(5)
Unrealized losses / (gains) on derivatives - net and from remeasurement of monetary assets and liabilities - net	11	(17)
Losses on disposal	0	2
Other - net	13	6
Interest paid	(73)	(78)
Income tax paid	18	(11)
Change in trade working capital
Inventories	35	24
Trade receivables	7	(29)
Trade payables	(18)	104
Margin calls	0	5
Change in provisions and pension obligations	2	(15)
Other working capital	15	3
Net cash flows from operating activities	152	260
Purchases of property, plant and equipment	(98)	(130)
Acquisition of subsidiaries net of cash acquired	0	(83)
Proceeds from disposals, net of cash	1	1
Other investing activities	0	(4)
Net cash flows used in investing activities	(97)	(216)
Proceeds from issuance of Senior Notes	290	0
Repayment of Senior Notes	(200)	0
Proceeds from French loan	180	0
Proceeds from Swiss credit facility	18	0
Lease repayments	(17)	(70)
(Repayments) / proceeds from U.S. revolving credit facility and other loans	(124)	76
Payment of deferred financing costs	(9)	0
Transactions with non-controlling interests	0	(2)
Other financing activities	2	0
Net cash flows from financing activities	140	4
Net increase in cash and cash equivalents	195	48
Cash and cash equivalents - beginning of year	184	164
Effect of exchange rate changes on cash and cash equivalents	(1)	1
Cash and cash equivalents - end of period	€ 378	€ 213

GENERAL INFORMATION

GENERAL INFORMATION	6 Months Ended
	Jun. 30, 2020
Disclosure of general information [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. The Group has a strategic footprint of manufacturing facilities located in North America, Europe and China and operates 28 production facilities, 3 administrative centers and 3 R&D centers. The Group has approximately 12,400 employees. Constellium SE, a French Societas Europaea (SE), is the parent company of the Group. The business address (head office) of Constellium SE is Washington Plaza, 40-44 rue Washington, 75008 Paris, France. 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, 2020
Disclosure of summary of significant accounting policies [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, 2020 and 2019 ; and the Unaudited Interim Consolidated Statement of Financial Position and Changes in Equity at June 30, 2020 and December 31, 2019 . 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, 2019 , which were authorized for issue by the Board of Directors on March 9, 2020. These Unaudited Condensed Interim Consolidated Financial Statements were authorized for issue by management on July 21, 2020. 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 financial position, its cash flows, liquidity position and borrowing facilities are described in the Unaudited Condensed Interim Consolidated Financial Statements in NOTE 10 - Cash and Cash Equivalent , NOTE 16 - Borrowings and NOTE 18 - Financial Risk Management . 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 this assumption is not invalidated by the Group’s negative equity at June 30, 2020 . 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, 2019 , except for the application of the effective tax rate in accordance with IAS 34 - Interim Financial Reporting . 2.3 Application of new and revised IFRS Several amendments and interpretations apply for the first time in 2020 , 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. The Group plans to adopt the new standards and interpretations on their required effective dates. 2.4 Presentation of the operating performance of each operating segment and of the Group In accordance with IFRS 8 - Operating Segments , operating segments are based upon the product lines, markets and industries served, and are reported in a manner consistent with the internal reporting provided to the chief operating decision-maker (“CODM”). The CODM, who is responsible for allocating resources and assessing performance of the operating segments, has been identified as the Chief Executive Officer. 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 and non-operating items. Adjusted EBITDA is defined as income / (loss) from continuing operations before income taxes, results from joint ventures, net finance costs, other expenses and depreciation and amortization as adjusted to exclude restructuring costs, impairment charges, unrealized gains or losses on derivatives and on foreign exchange differences on transactions that do not qualify for hedge accounting, metal price lag, share-based compensation expense, effects of certain purchase accounting adjustments, start-up and development costs or acquisition, integration and separation costs, certain incremental costs and other exceptional, unusual or generally non-recurring items. 2.5 Principles governing the preparation of the Unaudited Condensed Interim Consolidated Financial Statement The following table summarizes the main exchange rates used for the preparation of the Unaudited Condensed Interim Consolidated Financial Statements: Foreign exchange rate for 1 Euro Six months ended At June 30, Six months ended At December 31, Average rate Closing rate Average rate Closing rate U.S. Dollars USD 1.1018 1.1198 1.1297 1.1234 Swiss Francs CHF 1.0641 1.0651 1.1294 1.0854 Czech Koruna CZK 26.2970 26.7400 25.6842 25.4080 Presentation of financial statements The Unaudited Condensed Interim Consolidated Financial Statements are presented in millions of Euros, except Earnings per share, which is presented in Euros. Certain reclassifications may have been made to prior year amounts to conform to the current year presentation. 2.6 Judgments in applying accounting policies and key sources of estimation uncertainty The preparation of financial statements requires to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, revenue 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, 2019 . The Group reviewed these significant assumptions and estimates in light of the uncertainty associated with the Covid-19 downturn and its potential impact on the global economy and its business. The Group believes that the accounting assumptions and estimates used in the preparation of the Unaudited Condensed Interim Consolidated Financial Statements at and for the period ended June 30, 2020 are appropriate. However, there remains considerable uncertainty with respect to the duration of the crisis and its potential impact on the overall economy and our business and there can be no guarantee that our assumptions will materialize or that actual results will not differ materially from estimates. 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 2020 .

REVENUE

REVENUE	6 Months Ended
	Jun. 30, 2020
Revenue [abstract]
REVENUE	NOTE 3 - REVENUE 3.1 Disaggregation of revenue The following table presents our revenue by product line: (in millions of Euros) Three months ended Three months ended Six months ended Six months ended Packaging rolled products 456 568 980 1,116 Automotive rolled products 88 209 281 439 Specialty and other thin-rolled products 20 42 52 90 Aerospace rolled products 142 224 365 429 Transportation, Industry and other rolled products 105 148 231 310 Automotive extruded products 96 199 295 387 Other extruded products 124 148 264 303 Total Revenue 1,031 1,538 2,468 3,074 The following table presents our revenue by destination of shipment: (in millions of Euros) Three months ended Three months ended Six months ended Six months ended France 67 154 188 306 Germany 192 339 479 678 United Kingdom 39 49 108 99 Switzerland 15 18 27 38 Other Europe 201 286 476 555 United States 413 600 974 1,164 Canada 7 9 24 27 Asia and Other Pacific 61 68 118 137 All Other 36 15 74 70 Total Revenue 1,031 1,538 2,468 3,074 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, 2020
Disclosure of operating segments [abstract]
OPERATING SEGMENT INFORMATION	NOTE 4 - 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. 4.1 Segment Revenue Three months ended Three months ended Six months ended Six months ended (in millions of Euros) Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue P&ARP 565 (1 ) 564 821 (2 ) 819 1,317 (4 ) 1,313 1,649 (4 ) 1,645 A&T 250 (3 ) 247 383 (11 ) 372 609 (13 ) 596 761 (22 ) 739 AS&I 222 (2 ) 220 347 — 347 564 (5 ) 559 691 (1 ) 690 Holdings & Corporate — — — — — — — — — — — — Total 1,037 (6 ) 1,031 1,551 (13 ) 1,538 2,490 (22 ) 2,468 3,101 (27 ) 3,074 4.2 Segment Adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income (in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended P&ARP 58 79 124 138 A&T 31 64 83 116 AS&I (1 ) 30 33 59 Holdings & Corporate (7 ) (6 ) (12 ) (11 ) Adjusted EBITDA 81 167 228 302 Metal price lag (A) (25 ) (13 ) (40 ) (31 ) Start-up and development costs (B) (2 ) (3 ) (4 ) (5 ) Bowling Green one-time costs related to the acquisition (C) — — — (6 ) Share-based compensation costs (5 ) (4 ) (8 ) (7 ) Losses on pension plan amendments 19 (2 ) — (2 ) — Depreciation, amortization and impairment 13,14 (71 ) (60 ) (137 ) (117 ) Restructuring costs 20 (11 ) (1 ) (11 ) (1 ) Unrealized gains / (losses) on derivatives 5 43 (14 ) (10 ) 17 Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities – net 5 1 (1 ) (1 ) — Losses on disposals 5 — (1 ) — (2 ) Other (D) (10 ) (1 ) (10 ) (1 ) (Loss) / income from operations (1 ) 69 5 149 Finance costs - net 7 (42 ) (43 ) (87 ) (89 ) Share of income of joint-ventures — — — 5 (Loss) / income before income tax (43 ) 26 (82 ) 65 Income tax benefit / (expense) 8 11 (9 ) 19 (24 ) Net (loss) / income (32 ) 17 (63 ) 41 (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, 2020 and 2019 start-up and development costs included €4 million , and €5 million , respectively, related to new projects in our AS&I operating segment. (C) For the six months ended June 30, 2019, Bowling Green one-time costs related to the acquisition included the non-cash reversal of the inventory step-up. (D) For the six months ended June 30, 2020 , Other includes €5 million of procurement penalties and termination fees incurred because of the Group's inability to fulfill certain commitments due to the Covid-19 downturn and a €5 million loss resulting from the discontinuation of hedge accounting for certain forecasted sales that were determined to be no longer expected to occur in light of the Covid-19 downturn effects. 4.3 Segment capital expenditures (in millions of Euros) Six months ended Six months ended P&ARP (38 ) (44 ) A&T (24 ) (29 ) AS&I (34 ) (56 ) Holdings & Corporate (2 ) (1 ) Capital expenditures (98 ) (130 ) 4.4 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 1,969 1,951 A&T 818 856 AS&I 716 703 Holdings & Corporate 213 276 Segment assets 3,716 3,786 Deferred income tax assets 222 185 Cash and cash equivalents 378 184 Other financial assets 31 29 Total assets 4,347 4,184

OTHER GAINS _ (LOSSES)_NET

OTHER GAINS / (LOSSES)—NET	6 Months Ended
	Jun. 30, 2020
Analysis of income and expense [abstract]
OTHER GAINS / (LOSSES)—NET	NOTE 5 - OTHER GAINS / (LOSSES) - NET (in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended Realized losses on derivatives (A) (32 ) (14 ) (44 ) (28 ) Losses reclassified from OCI as a result of hedge accounting discontinuation (B) 4 (5 ) — (5 ) — Unrealized gains / (losses) on derivatives at fair value through profit and loss - net (A) 4 43 (14 ) (10 ) 17 Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities - net 4 1 (1 ) (1 ) — Losses on pension plan amendments 19 (2 ) — (2 ) — Losses on disposal 4 — (1 ) — (2 ) Other — — (1 ) (1 ) Total other gains / (losses) - net 5 (30 ) (63 ) (14 ) (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. (B) In the period ended June 30, 2020 , we determined that a portion of the hedged forecasted sales for the second half of 2020 and 2021, to which hedge accounting is applied, was no longer expected to occur. As a result, the f air value of the related derivatives accumulated in equity was reclassified in the Unaudited Interim Consolidated Income Statement and generated a €5 million loss.

CURRENCY GAINS _ (LOSSES)

CURRENCY GAINS / (LOSSES)	6 Months Ended
	Jun. 30, 2020
Analysis of income and expense [abstract]
CURRENCY GAINS / (LOSSES)	NOTE 6 - CURRENCY GAINS / (LOSSES) Currency gains and losses, which are included in Income from operations, are as follows: (in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended Included in Revenue 18 (2 ) (1 ) (5 ) (2 ) Included in Cost of sales 1 — 1 — Included in Other gains / (losses) - net (5 ) (1 ) (6 ) 4 Total (6 ) (2 ) (10 ) 2 Realized exchange (losses) / gains on foreign currency derivatives - net 18 (3 ) — (3 ) 1 Losses reclassified from OCI as a result of hedge accounting discontinuation 18 (5 ) — (5 ) — Unrealized (losses) / gains on foreign currency derivatives - net 18 — (1 ) (2 ) 1 Exchange gains / (losses) from the remeasurement of monetary assets and liabilities - net 2 (1 ) — — Total (6 ) (2 ) (10 ) 2 See NOTE 17 - Financial Instruments and NOTE 18 - 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, 2020
Analysis of income and expense [abstract]
FINANCE COSTS—NET	NOTE 7 - FINANCE COSTS - NET (in millions of Euros) Three months ended Three months ended Six months ended Six months ended Interest expense on borrowings (A) (30 ) (30 ) (61 ) (62 ) Expenses on factoring arrangements (3 ) (5 ) (6 ) (10 ) Interest expense on leases (2 ) (4 ) (5 ) (7 ) Realized and unrealized (losses) / gains on debt derivatives at fair value (B) (7 ) (4 ) 1 5 Realized and unrealized exchange gains / (losses) on financing activities - net (B) 8 6 (3 ) — Interest cost on pension and other benefits (3 ) (4 ) (6 ) (8 ) Other finance expenses (6 ) (2 ) (8 ) (8 ) Capitalized borrowing costs (C) 1 — 1 1 Finance expenses (42 ) (43 ) (87 ) (89 ) Finance costs - net (42 ) (43 ) (87 ) (89 ) (A) For the six months ended June 30, 2020 , the Group incurred mainly (i) €57 million of interest related to Constellium SE Senior Notes and (ii) €3 million of interest expense and fees related to the Muscle Shoals, Bowling Green and Ravenswood ABL Facility (“Pan-U.S. ABL”). 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) €3 million of interest expense and fees related to the Pan-U.S. ABL. (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) Borrowing costs directly attributable to the construction of assets are capitalized. The capitalization rate was 6% for the six months ended June 30, 2020 and 2019 .

INCOME TAX

INCOME TAX	6 Months Ended
	Jun. 30, 2020
Income Taxes [Abstract]
INCOME TAX	NOTE 8 - INCOME TAX Income tax benefit / (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 at June 30, 2020 is impacted by non-recurring transactions and subject to country mix effect. The assessment on net deferred tax assets was reviewed at June 30, 2020 using the same assumptions as the impairment tests in NOTE 13 - Property, Plant and Equipment , and considering changes in tax laws enacted during the six months ended June 30, 2020 . This review did not change the assessment made at December 31, 2019.

EARNINGS PER SHARE

EARNINGS PER SHARE	6 Months Ended
	Jun. 30, 2020
Earnings per share [abstract]
EARNINGS PER SHARE	NOTE 9 - EARNINGS PER SHARE (in millions of Euros) Three months ended Three months ended Six months ended Six months ended Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share (33 ) 16 (64 ) 39 Number of shares attributable to equity holders of Constellium (number of shares) Three months ended Three months ended Six months ended Six months ended Weighted average number of ordinary shares used to calculate basic earnings per share 137,901,336 136,700,491 137,903,307 136,344,030 Effect of other dilutive potential ordinary shares (A) — 3,620,938 — 4,005,235 Weighted average number of ordinary shares used to calculate diluted earnings per share 137,901,336 140,321,429 137,903,307 140,349,265 (A) For the six months and three months ended June 30, 2020 , there were 4,878,787 and 4,880,758 , potential ordinary shares that could have a dilutive impact, but were considered antidilutive due to negative earnings, respectively. For the six months and three months ended June 30, 2019 , dilutive potential new ordinary shares to be issued were part of share-based compensation plans. Earnings per share attributable to the equity holders of Constellium (in Euro per share) Three months ended Three months ended Six months ended Six months ended Basic (0.24 ) 0.12 (0.46 ) 0.29 Diluted (0.24 ) 0.11 (0.46 ) 0.28

CASH AND CASH EQUIVALENTS

CASH AND CASH EQUIVALENTS	6 Months Ended
	Jun. 30, 2020
Cash and cash equivalents [abstract]
CASH AND CASH EQUIVALENTS	NOTE 10 - CASH AND CASH EQUIVALENTS (in millions of Euros) At June 30, At December 31, Cash in bank and on hand 378 184 Total Cash and cash equivalent 378 184 At June 30, 2020 , cash in bank and on hand includes a total of €22 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. At December 31, 2019 , the amount subject to these restrictions was €22 million .

TRADE RECEIVABLES AND OTHER

TRADE RECEIVABLES AND OTHER	6 Months Ended
	Jun. 30, 2020
Trade and other receivables [abstract]
TRADE RECEIVABLES AND OTHER	NOTE 11 - TRADE RECEIVABLES AND OTHER Trade receivables and other are comprised of the following: At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Trade receivables - gross — 389 — 395 Impairment — (3 ) — (2 ) Total trade receivables - net — 386 — 393 Income tax receivables 34 9 35 22 Other taxes — 17 — 35 Contract assets 31 1 16 2 Prepaid expenses 1 20 1 8 Other 8 18 8 14 Total other receivables 74 65 60 81 Total trade receivables and other 74 451 60 474 11.1 Contract assets At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Unbilled tooling costs 14 — 16 — Other 17 1 — 2 Total Contract assets 31 1 16 2 11.2 Aging The aging of total trade receivables - net is as follows: (in millions of Euros) At June 30, At December 31, Not past due 369 380 1 – 30 days past due 15 10 31 – 60 days past due 2 3 61 – 90 days past due — — Greater than 90 days past due — — Total trade receivables - net 386 393 Impairment allowance Revisions to the impairment allowance arising from changes in estimates are included as either an additional allowance or a reversal. An allowance was recognized for €0.4 million net during the six months ended June 30, 2020 (an allowance of €0.1 million was recognized during the six months ended June 30, 2019 ). 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. 11.3 Currency concentration The composition of the carrying amounts of total Trade receivables - net by currency is shown in Euro equivalents as follows: (in millions of Euros) At June 30, At December 31, Euro 158 126 U.S. Dollar 203 251 Swiss franc 14 3 Other currencies 11 13 Total trade receivables - net 386 393 11.4 Factoring arrangements The Group factors trade receivables in France through factoring agreement with a third party for a maximum capacity of €255 million . This agreement matures on December 31, 2023 . The Group factors trade receivables in Germany, Switzerland and Czech Republic through factoring agreements with a third party for a maximum capacity of €150 million . These agreements mature on December 31, 2023 . 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. In addition, Constellium Valais is party to an uncommitted factoring arrangement which provides for the sale of specific customer receivables. Constellium Automotive USA LLC is party to a factoring agreement which provides for the sale of specific account receivables up to a maximum capacity of $25 million . This agreement matures on December 10, 2020. Muscle Shoals is party to a factoring agreement that provides for the sale of specific trade receivables up to a maximum capacity of $300 million . This agreement matures on September 30, 2021. 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, as the Group retains substantially all the associated risks and rewards. Under the agreements, at June 30, 2020 , the total carrying amount of the original assets factored is €506 million ( December 31, 2019 : €574 million ) of which: • €390 million ( December 31, 2019 : €463 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; • €116 million ( December 31, 2019 : €111 million ) were recognized on the Unaudited Condensed Interim Consolidated Statement of Financial Position. There was a €7 million debt due to the factors relating to trade account receivables sold at June 30, 2020 , and no debt at December 31, 2019 . 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 certain credit ratings being maintained. The Group was in compliance with all applicable covenants at June 30, 2020 and December 31, 2019 .

INVENTORIES

INVENTORIES	6 Months Ended
	Jun. 30, 2020
Subclassifications of assets, liabilities and equities [abstract]
INVENTORIES	NOTE 12 - INVENTORIES (in millions of Euros) At June 30, At December 31, Finished goods 194 203 Work in progress 303 321 Raw materials 99 106 Stores and supplies 77 74 Inventories write-down (38 ) (34 ) Total inventories 635 670 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, 2020
Property, plant and equipment [abstract]
PROPERTY, PLANT AND EQUIPMENT	NOTE 13 - PROPERTY, PLANT AND EQUIPMENT (in millions of Euros) Land and Property Rights Buildings Machinery and Equipment Construction Work in Progress Other Total Net balance at January 1, 2020 19 366 1,451 203 17 2,056 Additions — 9 36 66 1 112 Disposals — — (2 ) — — (2 ) Depreciation and impairment — (14 ) (108 ) (5 ) (5 ) (132 ) Transfer during the year 2 18 52 (74 ) 2 — Effects of changes in foreign exchange rates — (1 ) — (2 ) — (3 ) Net balance at June 30, 2020 21 378 1,429 188 15 2,031 Cost 37 552 2,488 198 47 3,322 Less accumulated depreciation and impairment (16 ) (174 ) (1,059 ) (10 ) (32 ) (1,291 ) Net balance at June 30, 2020 21 378 1,429 188 15 2,031 Right of use assets Right of use have been included within the same line item as that within which the corresponding underlying assets would be presented if they were owned. (in millions of Euros) Buildings Machinery and Equipment Other Total Net balance at January 1, 2020 116 71 3 190 Additions 9 10 1 20 Disposals (1 ) — — (1 ) Depreciation (6 ) (11 ) (1 ) (18 ) Effects of changes in foreign exchange rates — (1 ) — (1 ) Net balance at June 30, 2020 118 69 3 190 Cost 142 121 5 268 Less accumulated depreciation and impairment (24 ) (52 ) (2 ) (78 ) Net balance at June 30, 2020 118 69 3 190 The total expense relating to short-term leases, low value asset leases and variable lease payments that are still recognized as operating expenses was €6 million and €7 million for the six months ended June 30, 2020 and 2019 , respectively. Impairment tests for property, plant and equipment and intangibles assets (including goodwill) The Covid-19 downturn, which resulted in a temporary shutdown of some of our plants and is expected to negatively impact our future operating profits and cash flows, was identified as an indicator of impairment for all of Constellium Cash Generating Units (“CGUs”) and group of CGUs at March 31, 2020. Consequently, in accordance with the accounting policies described in Note 2.6 of the Consolidated Financial Statements, all our CGUs and group of CGUs to which goodwill is allocated were tested for impairment at March 31, 2020. For the three months ended June 30, 2020 , management reviewed the impairment test assumptions and did not identify any indicator of impairment on any of its CGUs except for Nanjing. As a result of these tests, management concluded that no impairment charge was required on any of its CGUs except for Nanjing. In performing our impairment tests, the following assumptions were factored in: • Operating levels of our plants at 50% of capacity on average during three months in 2020, • Significant economic downturn in our automotive and aerospace markets in the period 2020 to 2023, • Positive impact of counter-measures implemented or planned, including reductions in capital expenditures and costs. • The assessment that our strategy, which is grounded notably in the long term competitive advantage of aluminium and the uniqueness of our assets, remained intact despite the Covid-19 downturn. In June 2020, the main customer of the Nanjing Automotive Structures plant (China) announced a suspension of its operations and a strategic reorganization. As a result, we tested the asset for impairment and recorded an impairment charge of €5 million for the six months ended June 30, 2020 .

INTANGIBLE ASSETS (INCLUDING GO

INTANGIBLE ASSETS (INCLUDING GOODWILL)	6 Months Ended
	Jun. 30, 2020
Intangible assets and goodwill [abstract]
INTANGIBLE ASSETS (INCLUDING GOODWILL)	NOTE 14 - INTANGIBLE ASSETS (INCLUDING GOODWILL) (in millions of Euros) Goodwill Technology Computer Software Customer relationships Work in Progress Other Total intangible assets (excluding goodwill) Net balance at January 1, 2020 455 21 19 14 14 2 70 Additions — — — — 3 — 3 Amortization expense — (1 ) (4 ) — — — (5 ) Transfer during the year — — 1 — (1 ) — — Effects of changes in foreign exchange rates 1 — — — — — — Net balance at June 30, 2020 456 20 16 14 16 2 68 Cost 456 86 75 40 17 2 220 Less accumulated depreciation and impairment — (66 ) (59 ) (26 ) (1 ) — (152 ) Net balance at June 30, 2020 456 20 16 14 16 2 68

TRADE PAYABLES AND OTHER

TRADE PAYABLES AND OTHER	6 Months Ended
	Jun. 30, 2020
Trade and other payables [abstract]
TRADE PAYABLES AND OTHER	NOTE 15 - TRADE PAYABLES AND OTHER At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Trade payables — 683 — 711 Fixed assets payables — 29 — 43 Employees' entitlements — 173 — 171 Taxes payable other than income tax — 33 — 14 Contract liabilities and other liabilities to customers 5 78 6 54 Other payables 14 7 15 6 Total other 19 320 21 288 Total trade payables and other 19 1,003 21 999 Contract liabilities At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Deferred tooling revenue 2 — 2 — Advance payment from customers 1 4 2 5 Unrecognized variable consideration (A) 2 57 2 46 Other — 17 — 3 Total contract liabilities and other liabilities to customers 5 78 6 54 (A) Unrecognized variable consideration consists of expected volume rebates, discounts, incentives, refunds, penalties and price concessions. For the six months ended June 30, 2020 , €14 million of revenue that related to contract liabilities at December 31, 2019 was recognized. Revenue of €25 million generated in the six months ended June 30, 2020 was deferred.

BORROWINGS

BORROWINGS	6 Months Ended
	Jun. 30, 2020
Borrowings [abstract]
BORROWINGS	NOTE 16 - BORROWINGS 16.1 Analysis by nature (in millions of Euros) At June 30, At December 31, Nominal Value in Currency Nominal rate Effective rate Nominal Value In Euros (Arrangement fees) Accrued interests Carrying value Carrying value Secured Pan-U.S. ABL $ — Floating 3.43 % — — — — 127 Secured U.S. DDTL $ — Floating — — — — — — Secured French Loan € 180 Floating 2.50 % 180 — — 180 — Secured Inventory Based Facility (due 2021) — Floating — — — — — — Senior Unsecured Notes Constellium SE $ 400 5.75 % 6.26 % 357 (3 ) 3 357 355 Constellium SE € — 4.63 % 5.16 % — — — — 200 Constellium SE $ 650 6.63 % 7.13 % 580 (9 ) 13 584 582 Constellium SE $ 500 5.88 % 6.26 % 447 (6 ) 10 451 449 Constellium SE € 400 4.25 % 4.57 % 400 (5 ) 6 401 400 Constellium SE $ 325 5.63 % 6.05 % 290 (6 ) — 284 — Unsecured Revolving Credit Facility (due 2021) (D) — Floating — — — — — — Unsecured Credit facility Switzerland (due 2025) (E) CHF 20 1.18 % 1.18 % 18 — — 18 — Lease liabilities 190 — 1 191 188 Other loans (F) 68 — 2 70 60 Total Borrowings 2,530 (29 ) 35 2,536 2,361 Of which non-current 2,434 2,160 Of which current 102 201 Constellium SE Senior Notes are guaranteed by certain subsidiaries. (A) On April 24, 2020, Constellium Muscle Shoals, Constellium Rolled Product Ravenswood, LLC and Constellium Bowling Green amended the Pan-U.S. ABL to include a delay-draw term loan (the “ U.S. DDTL ” ) of $166 million . (B) On May 13, 2020, one of our French entities entered into a term facility agreement with a syndicate of banks (the “French Loan”), 80% guaranteed by the French State. The French Loan established a fully committed term loan for an aggregate amount up to €180 million , of which €30 million was provided by Bpifrance Financement, a related party. The French Loan will mature no earlier than May 20, 2021, and the Company has the option to extend it for up to five years . (C) On June 30, 2020, Constellium SE issued $325 million principal amount of the 5.625% Senior Notes due 2028. Deferred arrangement fees amounted to €6 million on the issuance date. A portion of the net proceeds from the issuance were used to repurchase the remaining €200 million of the 4.625% Constellium SE Senior Unsecured Notes issued in May 2014, due 2021. (D) The Unsecured Revolving Credit Facility has a €5 million borrowing base and is provided by Bpifrance Financement, a related party. (E) On May 22, 2020, Constellium Valais entered into an uncommitted revolving credit facility for an amount of CHF 20 million , 85% guaranteed by the Swiss state. This facility may be terminated by either party at any time. (F) Other loans include €38 million of financial liabilities relating to the sale and leaseback of assets that were considered to be financing arrangements in substance. 16.2 Movements in borrowings (in millions of Euros) Six months ended Year ended December 31,2019 At December 31, prior year 2,361 2,151 IFRS 16 application — 102 At January 1 2,361 2,253 Cash flows Proceeds from issuance of Senior Notes (A) 290 — Repayment of Senior Notes (B) (200 ) (100 ) Proceeds from French loan 180 — Proceeds from Swiss credit facility 18 — (Repayments) / proceeds from U.S. revolving credit facility and other loans (124 ) 109 Payment of deferred financing costs (6 ) — Lease repayments (17 ) (86 ) Non-cash changes Borrowings assumed through business combination — 75 Movement in interests accrued or capitalized (1 ) 1 New leases and other loans 25 75 Deferred arrangement fees and other 3 5 Effects of changes in foreign exchange rates 7 29 At the end of the period 2,536 2,361 (A) The proceeds from the Senior Notes issued on June 30, 2020 were €290 million , converted at the issuance date exchange rate of EUR/USD= 1.1198 . (B) On June 30, 2020, the remaining €200 million of the 4.625% Senior Notes due 2021 were redeemed. On August 8, 2019, €100 million of the €300 million outstanding aggregate principal amount of the 4.625% Senior Notes due 2021 were redeemed. 16.3 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 1,757 1,597 Euro 741 746 Other currencies 38 18 Total borrowings 2,536 2,361 Covenants The Group was in compliance with all applicable debt covenants at June 30, 2020 and December 31, 2019 , and for the six months ended June 30, 2020 and the year ended December 31, 2019 . 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. ABL Facility This facility contains a fixed charge coverage ratio covenant and an EBITDA contribution ratio covenant along with customary affirmative and negative covenants. Evaluation of compliance with the maintenance covenants is only required if the excess availability falls below 10% of the aggregate revolving loan commitment. French Loan The French loan contains financial covenants that provide that, on semi-annual testing dates beginning June 30, 2021: (i) the net debt leverage shall not exceed a specified ratio and (ii) the interest cover ratio is at least equal to a specified ratio. The French loan also contains customary terms and conditions, including, among other things, negative covenants, limitation on incurring debt, selling assets, certain corporate transactions and reorganizations, making loans and advances and entering into certain derivative transactions.

FINANCIAL INSTRUMENTS

FINANCIAL INSTRUMENTS	6 Months Ended
	Jun. 30, 2020
Disclosure of detailed information about financial instruments [abstract]
FINANCIAL INSTRUMENTS	NOTE 17 - FINANCIAL INSTRUMENTS 17.1 Financial assets and liabilities by categories At June 30, At December 31, (in millions of Euros) Notes At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total Cash and cash equivalents 10 378 — — 378 184 — — 184 Trade receivables 11 — — 386 386 — — 393 393 Other financial assets — 31 — 31 — 29 — 29 Total 378 31 386 795 184 29 393 606 At June 30, At December 31, (in millions of Euros) Notes At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total Trade payables and fixed assets payables 15 712 — — 712 754 — — 754 Borrowings 16 2,536 — — 2,536 2,361 — — 2,361 Other financial liabilities — 61 14 75 — 44 14 58 Total 3,248 61 14 3,323 3,115 44 14 3,173 The table below details other financial assets and other financial liabilities positions: At June 30, At December 31, (in millions of Euros) Non-current Current Total Non-current Current Total Derivatives 9 22 31 7 22 29 Aluminium and premium future contracts 2 11 13 1 8 9 Energy future contracts — — — — — — Other future contracts — — — — — — Currency commercial contracts 7 10 17 5 12 17 Currency net debt derivatives — 1 1 1 2 3 Other financial assets 9 22 31 7 22 29 Derivatives 30 45 75 23 35 58 Aluminium and premium future contracts 9 19 28 4 10 14 Energy future contracts — — — — 1 1 Other future contracts 1 4 5 2 4 6 Currency commercial contracts 15 21 36 12 16 28 Currency net debt derivatives 5 1 6 5 4 9 Other financial liabilities 30 45 75 23 35 58 17.2 Fair values All derivatives are presented at fair value in the Unaudited Condensed 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, November 2017 and June 2020 account for 100.5% , 101.6% , 99.7% and 99.8% respectively of the nominal value and amount to €359 million , €589 million , €844 million and €289 million respectively, at June 30, 2020 . 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. 17.3 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 a quoted price (unadjusted) in active markets for identical financial instruments. Level 1 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). Level 2 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, At December 31, (in millions of Euros) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Other financial assets - derivatives 12 19 — 31 8 21 — 29 Other financial liabilities - derivatives 30 45 — 75 19 39 — 58 There was no transfer of asset and liability categories into or out of Level 1, Level 2 or Level 3 during the six months ended June 30, 2020 and the year ended December 31, 2019 .

FINANCIAL RISK MANAGEMENT

FINANCIAL RISK MANAGEMENT	6 Months Ended
	Jun. 30, 2020
Disclosure of financial risk management [Abstract]
FINANCIAL RISK MANAGEMENT	NOTE 18 - 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 strategy. 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. 18.1 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 which 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 $109 million , at June 30, 2020 ( $233 million at December 31, 2019 ), and maturities from 2020 to 2022 . In May 2020, the Group signed a new contract with the same major customer and entered into foreign exchange derivatives that were designated for hedge accounting, with total nominal amount of $255 million at June 30, 2020 , maturing from 2022 to 2025 . For hedges that do not qualify for hedge accounting, any mark-to-market movements are recognized in Other gains / (losses) - net. The table below details the effect of foreign currency derivatives in the Unaudited Interim Consolidated Income Statement and the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss): (in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended Derivatives that do not qualify for hedge accounting Included in Other gains / (losses) - net Realized gains on foreign currency derivatives - net 6 — 1 2 3 Unrealized (losses) / gains on foreign currency derivatives - net (A) 6 (1 ) (1 ) (2 ) 1 Derivatives that qualify for hedge accounting Included in Revenue Realized losses on foreign currency derivatives - net 6 (3 ) (1 ) (5 ) (2 ) Unrealized gains on foreign currency derivatives - net 6 1 — — — Included in Other gains / (losses) - net Losses reclassified from OCI as a result of hedge accounting discontinuation (B) 6 (5 ) — (5 ) — Included in Other comprehensive income / (loss) — Unrealized gains / (losses) on foreign currency derivatives - net 2 1 (6 ) (7 ) Gains reclassified from cash flow hedge reserve to the Unaudited Interim Consolidated Income Statement 3 1 6 2 (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 years when these sales are recognized. (B) In the period ended June 30, 2020 , we determined that a portion of the hedged forecasted sales for the second half of 2020 and 2021, to which hedge accounting is applied, was no longer expected to occur. As a result, the f air value of the related derivatives accumulated in equity was reclassified in the Unaudited Interim Consolidated Income Statement and generated a €5 million loss. 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 CHF 174 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 loss of the net investment hedge realized in 2019 was included in Currency translation differences within Other comprehensive income for €3 million . 18.3 Liquidity and capital risk management The liquidity requirements of the overall Company are funded by drawing on available cash and 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, 2020 , the borrowing base was $322 million for the Pan-U.S. ABL, $166 million for the U.S. DDTL , and €78 million for the French Inventory Based Facility. After the deduction of amounts drawn and letters of credit, the Group had €506 million of outstanding availability under these facilities at June 30, 2020 . At December 31, 2019 , the borrowing base for the Pan-U.S. ABL and the French Inventory Based Facility were $375 million and €82 million , respectively. After the deduction of amounts drawn and letters of credit, the Group had €281 million of outstanding availability under these facilities at December 31, 2019 . At June 30, 2020 , liquidity was €949 million , comprised of €378 million of cash and cash equivalents and €571 million of available undrawn facilities, including the €506 million described above. At December 31, 2019 , liquidity was €516 million , comprised of €184 million of cash and cash equivalents and €332 million of available undrawn facilities, including the €281 million described above.

PENSIONS AND OTHER POST-EMPLOYM

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS	6 Months Ended
	Jun. 30, 2020
Disclosure of employee benefits [Abstract]
PENSION AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS	NOTE 19 - PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS 19.1 Actuarial assumptions Pension and other post-employment benefit obligations were updated based on the discount rates applicable at June 30, 2020 . At June 30, At December 31, Switzerland 0.20% 0.15% US Hourly pension 2.70% - 2.85% 3.15% - 3.25% Salaried pension 2.75% 3.25% OPEB 2.70% - 3.00% 3.20% - 3.40% Other benefits 2.45% - 2.75% 3.00% - 3.20% France Retirements 0.95% 0.95% Other benefits 0.85% 0.80% Germany 1.05% 1.00% 19.2 Amounts recognized in the Unaudited Interim Consolidated Statement of Financial Position At June 30, At December 31, (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Present value of funded obligation 789 — 789 768 — 768 Fair value of plan assets (435 ) — (435 ) (445 ) — (445 ) Deficit of funded plans 354 — 354 323 — 323 Present value of unfunded obligation 131 230 361 127 220 347 Net liability arising from defined benefit obligation 485 230 715 450 220 670 19.3 Amounts recognized in the Unaudited Interim Consolidated Income Statement Three months ended Three months ended (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Service cost Current service cost (5 ) (1 ) (6 ) (5 ) (1 ) (6 ) Past service cost — (2 ) (2 ) — — — Net interest (2 ) (1 ) (3 ) (2 ) (2 ) (4 ) Immediate recognition of gains / (losses) arising over the period — (1 ) (1 ) — (2 ) (2 ) Administration expenses (1 ) — (1 ) — — — Total (8 ) (5 ) (13 ) (7 ) (5 ) (12 ) Six months ended Six months ended (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Service cost Current service cost (11 ) (3 ) (14 ) (9 ) (3 ) (12 ) Past service cost — (2 ) (2 ) — — — Net interest (3 ) (3 ) (6 ) (4 ) (4 ) (8 ) Immediate recognition of gains / (losses) arising over the period — — — — (2 ) (2 ) Administration expenses (1 ) — (1 ) (1 ) — (1 ) Total (15 ) (8 ) (23 ) (14 ) (9 ) (23 ) 19.4 Movement in net defined benefit obligations At June 30, Defined benefit obligations Plan Assets Net defined benefit liability (in millions of Euros) Pension benefits Other benefits Total At January 1, 2020 895 220 1,115 (445 ) 670 Included in the Unaudited Interim Consolidated Income Statement Current service cost 11 3 14 — 14 Interest cost / (income) 7 3 10 (4 ) 6 Past service cost — 2 2 — 2 Immediate recognition of gains / (losses) arising over the year — — — — — Administration expenses — — — 1 1 Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) Remeasurements due to: —actual return less interest on plan assets — — — 13 13 —changes in financial assumptions 16 11 27 — 27 —changes in demographic assumptions — — — — — —experience losses 1 (1 ) — — — Effects of changes in foreign exchange rates 6 1 7 (5 ) 2 Included in the Unaudited Interim Consolidated Statement of Cash Flows Benefits paid (18 ) (9 ) (27 ) 17 (10 ) Contributions by the Group — — — (10 ) (10 ) Contributions by the plan participants 2 — 2 (2 ) — At June 30, 2020 920 230 1,150 (435 ) 715 Ravenswood OPEB disputes In 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. This change in benefits resulted in the recognition of a gain of €36 million from negative past service cost, which was lowered by €3 million in 2019 and €2 million in the second quarter of 2020, to reflect delays in the estimated implementation timetable. The United Steelworkers Local Union 5668 (the “Union”) is contesting the OPEB Amendments and filed a lawsuit against Constellium Rolled Products Ravenswood, LLC ("Ravenswood") 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 Ravenswood from implementing the OPEB amendments pending resolution in arbitration. In September 2019, the arbitrator issued a decision ruling against Ravenswood and sustaining the Union’s grievance. Ravenswood filed a motion to vacate this decision, which was denied in June 2020. The Group intends to vigorously defend this case as it believes it has a strong legal position and it is probable that Ravenswood will ultimately prevail and be able to implement the OPEB amendments. Additionally, during 2019, the Union filed a grievance disputing the existing limitation of Ravenswood’s liability for the healthcare costs of pre-Medicare retirees. This matter is scheduled to be arbitrated in the coming months and the Group believes it is without merit and intends to defend it vigorously. 19.5 Net defined benefit obligations by country At June 30, At December 31, (in millions of Euros) Defined benefit obligations Plan assets Net defined benefit liability Defined benefit obligations Plan assets Net defined benefit liability France 164 (3 ) 161 161 (3 ) 158 Germany 140 (1 ) 139 144 (1 ) 143 Switzerland 303 (213 ) 90 299 (214 ) 85 United States 542 (218 ) 324 510 (227 ) 283 Other countries 1 — 1 1 — 1 Total 1,150 (435 ) 715 1,115 (445 ) 670

PROVISIONS

PROVISIONS	6 Months Ended
	Jun. 30, 2020
Disclosure of other provisions [abstract]
PROVISIONS	NOTE 20 - PROVISIONS (in millions of Euros) Notes Close down and environmental remediation costs Restructuring Legal claims Total At January 1, 2020 90 4 28 122 Allowance — 11 2 13 Amounts used — (5 ) — (5 ) Unused amounts reversed — — (4 ) (4 ) Unwinding of discounts 1 — — 1 Effects of changes in foreign exchange rates 1 — — 1 At June 30, 2020 92 10 26 128 Current 7 9 13 29 Non-Current 85 1 13 99 Total Provisions 92 10 26 128 Restructuring costs For the six months ended June 30, 2020 , restructuring costs amounted to €11 million and included mostly allowance of provisions associated with headcount reductions in Europe and in the U.S. Legal claims and other costs (in millions of Euros) At June 30, At December 31, Litigation 19 21 Disease claims 4 4 Other 3 3 Total Provisions for legal claims and other costs 26 28 Contingencies The Group is involved, and may become involved, in various lawsuits, claims and proceedings relating to customer claims, product liability, employee and retiree benefit matters 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 was subject to an arbitration by a customer claiming that Constellium had supplied defective products as a result of which the customer alleged it had suffered significant damages. The Group considered that this claim was without merit on both technical and legal grounds and believed it was not probable that the claim would result in a loss. This matter was satisfactorily resolved during the three months ended June 30, 2020.

NON-CASH INVESTING AND FINANCIN

NON-CASH INVESTING AND FINANCING TRANSACTIONS	6 Months Ended
	Jun. 30, 2020
Disclosure of cash flow statement [Abstract]
NON-CASH INVESTING AND FINANCING TRANSACTIONS	NOTE 21 - NON-CASH INVESTING AND FINANCING TRANSACTIONS Property, plant and equipment acquired through leases or financed by third parties amounted to €25 million and €33 million for the six months ended June 30, 2020 , and 2019 , respectively. These leases and financings are excluded from the Unaudited interim Statement of Cash Flow as they are non-cash investing transactions. The fair value of vested Restricted Stock Units and Performance Stock Units was zero for the six months ended June 30, 2020 , and amounted to €4 million for the six months ended June 30, 2019 . They are excluded from the Unaudited Interim Statement of Cash Flows as non-cash financing activities.

SHARE CAPITAL

SHARE CAPITAL	6 Months Ended
	Jun. 30, 2020
Disclosure of share capital, reserves and other equity interest [Abstract]
SHARE CAPITAL	NOTE 22 - SHARE CAPITAL At June 30, 2020 , the share capital amounted to €2,758,440.64 , divided into 137,922,032 ordinary shares, each with a nominal value of two cents , fully paid-up and of the same class. All shares have the right to one vote. (in millions of Euros) Number of shares Share capital Share premium At January 1, 2020 137,867,418 3 420 New shares issued 54,614 — — At June 30, 2020 137,922,032 3 420

SHARE-BASED COMPENSATION

SHARE-BASED COMPENSATION	6 Months Ended
	Jun. 30, 2020
Share-based payment arrangements [Abstract]
SHARE-BASED COMPENSATION	NOTE 23 - SHARE-BASED COMPENSATION Description of plans granted Performance-Based Restricted Stock Units (equity-settled) In April 2020, the Company granted 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 • A performance condition, contingent 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 200% . The following table lists the inputs to the model used for the PSUs granted in April 2020: Six months ended Fair value at grant date (in euros) 6.65 Share price at grant date (in euros) 4.64 Dividend yield — Expected volatility (A) 63 % Risk-free interest rate (US government bond yield) 0.36 % Model used Monte Carlo Restricted Stock Units Award Agreements (equity-settled) During the six months ended June 30, 2020 , the Company granted Restricted Stock Units (RSUs) to a certain number of employees subject to the beneficiaries remaining continuously employed within the Group from the grant date through the end of the vesting period. Vesting period is three years . The fair value of RSUs awarded under the plan described above is the quoted market price 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 potential ordinary share at the grant date. The total expense related to the potential ordinary shares amounted to €8 million and €7 million for the six months ended June 30, 2020 , and June 30, 2019 , respectively. Movement of potential shares The following table illustrates the number and movements in potential shares: Performance Share Units (PSUs) Restricted Stock Units (RSUs) Equity Award Plans Total Potential Shares At December 31, 2019 2,519,294 2,066,503 79,526 4,665,323 Granted (A) 1,049,839 910,047 — 1,959,886 Vested — (8,000 ) (46,614 ) (54,614 ) Forfeited (B) (46,306 ) (50,931 ) — (97,237 ) At June 30, 2020 3,522,827 2,917,619 32,912 6,473,358 (A) For PSUs, the number of potential shares granted is presented using a vesting multiplier of 100% . (B) For potential shares related to PSUs, 46,306 were forfeited following the departure of certain beneficiaries and none were forfeited in relation to the non-fulfilment of performance conditions.

COVID-19-RELATED GOVERNMENT ASS

COVID-19-RELATED GOVERNMENT ASSISTANCE	6 Months Ended
	Jun. 30, 2020
Government Assistance [Abstract]
COVID-19-RELATED GOVERNMENT ASSISTANCE	NOTE 24 - COVID-19-RELATED GOVERNMENT ASSISTANCE In the period ended June 30, 2020, the Group received government assistance in various forms, including government-guaranteed facilities in France, Germany, and Switzerland (see NOTE 16 - Borrowings and NOTE 25 - Subsequent Events ), as well as subsidies to compensate for the cost of employees furloughed as a result of the Covid-19 downturn in various jurisdictions. These subsidies were recognized where there was reasonable assurance that they would be received and all attached conditions would be complied with. For the six months ended June 30, 2020, Covid-19-related subsidies in the amount of €14 million were accounted for as a deduction of employee costs.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	6 Months Ended
	Jun. 30, 2020
Disclosure of non-adjusting events after reporting period [abstract]
SUBSEQUENT EVENTS	NOTE 25 - SUBSEQUENT EVENTS On July 15, 2020, Constellium Singen GmbH and Constellium Singen Rolled Products entered into two credit facilities 80% guaranteed by the German State, for a total amount of €50 million .

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2020
Disclosure of summary of significant accounting policies [abstract]
Statement of compliance	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, 2020 and 2019 ; and the Unaudited Interim Consolidated Statement of Financial Position and Changes in Equity at June 30, 2020 and December 31, 2019 . 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, 2019 , which were authorized for issue by the Board of Directors on March 9, 2020. These Unaudited Condensed Interim Consolidated Financial Statements were authorized for issue by management on July 21, 2020.
Basis of preparation	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 financial position, its cash flows, liquidity position and borrowing facilities are described in the Unaudited Condensed Interim Consolidated Financial Statements in NOTE 10 - Cash and Cash Equivalent , NOTE 16 - Borrowings and NOTE 18 - Financial Risk Management . 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 this assumption is not invalidated by the Group’s negative equity at June 30, 2020 . 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, 2019 , except for the application of the effective tax rate in accordance with IAS 34 - Interim Financial Reporting .
Application of new and revised IFRS	Application of new and revised IFRS Several amendments and interpretations apply for the first time in 2020 , 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. The Group plans to adopt the new standards and interpretations on their required effective dates.
Presentation of the operating performance of each operating segment and of the Group	Presentation of the operating performance of each operating segment and of the Group In accordance with IFRS 8 - Operating Segments , operating segments are based upon the product lines, markets and industries served, and are reported in a manner consistent with the internal reporting provided to the chief operating decision-maker (“CODM”). The CODM, who is responsible for allocating resources and assessing performance of the operating segments, has been identified as the Chief Executive Officer. 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 and non-operating items. Adjusted EBITDA is defined as income / (loss) from continuing operations before income taxes, results from joint ventures, net finance costs, other expenses and depreciation and amortization as adjusted to exclude restructuring costs, impairment charges, unrealized gains or losses on derivatives and on foreign exchange differences on transactions that do not qualify for hedge accounting, metal price lag, share-based compensation expense, effects of certain purchase accounting adjustments, start-up and development costs or acquisition, integration and separation costs, certain incremental costs and other exceptional, unusual or generally non-recurring items.
Presentation of financial statements	Presentation of financial statements The Unaudited Condensed Interim Consolidated Financial Statements are presented in millions of Euros, except Earnings per share, which is presented in Euros. Certain reclassifications may have been made to prior year amounts to conform to the current year presentation.
Judgments in applying accounting policies and key sources of estimation uncertainty	Judgments in applying accounting policies and key sources of estimation uncertainty The preparation of financial statements requires to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, revenue 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, 2019 . The Group reviewed these significant assumptions and estimates in light of the uncertainty associated with the Covid-19 downturn and its potential impact on the global economy and its business. The Group believes that the accounting assumptions and estimates used in the preparation of the Unaudited Condensed Interim Consolidated Financial Statements at and for the period ended June 30, 2020 are appropriate. However, there remains considerable uncertainty with respect to the duration of the crisis and its potential impact on the overall economy and our business and there can be no guarantee that our assumptions will materialize or that actual results will not differ materially from estimates. 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 2020 .

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of summary of significant accounting policies [abstract]
Schedule of Main Exchange Rates Used for Preparation of Financial Statements	The following table summarizes the main exchange rates used for the preparation of the Unaudited Condensed Interim Consolidated Financial Statements: Foreign exchange rate for 1 Euro Six months ended At June 30, Six months ended At December 31, Average rate Closing rate Average rate Closing rate U.S. Dollars USD 1.1018 1.1198 1.1297 1.1234 Swiss Francs CHF 1.0641 1.0651 1.1294 1.0854 Czech Koruna CZK 26.2970 26.7400 25.6842 25.4080

REVENUE (Tables)

REVENUE (Tables)	6 Months Ended
	Jun. 30, 2020
Revenue [abstract]
Schedule of Disaggregation Revenue	The following table presents our revenue by product line: (in millions of Euros) Three months ended Three months ended Six months ended Six months ended Packaging rolled products 456 568 980 1,116 Automotive rolled products 88 209 281 439 Specialty and other thin-rolled products 20 42 52 90 Aerospace rolled products 142 224 365 429 Transportation, Industry and other rolled products 105 148 231 310 Automotive extruded products 96 199 295 387 Other extruded products 124 148 264 303 Total Revenue 1,031 1,538 2,468 3,074 The following table presents our revenue by destination of shipment: (in millions of Euros) Three months ended Three months ended Six months ended Six months ended France 67 154 188 306 Germany 192 339 479 678 United Kingdom 39 49 108 99 Switzerland 15 18 27 38 Other Europe 201 286 476 555 United States 413 600 974 1,164 Canada 7 9 24 27 Asia and Other Pacific 61 68 118 137 All Other 36 15 74 70 Total Revenue 1,031 1,538 2,468 3,074

OPERATING SEGMENT INFORMATION (

OPERATING SEGMENT INFORMATION (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of operating segments [abstract]
Schedule of Segment Revenue	Three months ended Three months ended Six months ended Six months ended (in millions of Euros) Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue Segment revenue Inter-segment elimination External revenue P&ARP 565 (1 ) 564 821 (2 ) 819 1,317 (4 ) 1,313 1,649 (4 ) 1,645 A&T 250 (3 ) 247 383 (11 ) 372 609 (13 ) 596 761 (22 ) 739 AS&I 222 (2 ) 220 347 — 347 564 (5 ) 559 691 (1 ) 690 Holdings & Corporate — — — — — — — — — — — — Total 1,037 (6 ) 1,031 1,551 (13 ) 1,538 2,490 (22 ) 2,468 3,101 (27 ) 3,074
Schedule of Segment Adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income	(in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended P&ARP 58 79 124 138 A&T 31 64 83 116 AS&I (1 ) 30 33 59 Holdings & Corporate (7 ) (6 ) (12 ) (11 ) Adjusted EBITDA 81 167 228 302 Metal price lag (A) (25 ) (13 ) (40 ) (31 ) Start-up and development costs (B) (2 ) (3 ) (4 ) (5 ) Bowling Green one-time costs related to the acquisition (C) — — — (6 ) Share-based compensation costs (5 ) (4 ) (8 ) (7 ) Losses on pension plan amendments 19 (2 ) — (2 ) — Depreciation, amortization and impairment 13,14 (71 ) (60 ) (137 ) (117 ) Restructuring costs 20 (11 ) (1 ) (11 ) (1 ) Unrealized gains / (losses) on derivatives 5 43 (14 ) (10 ) 17 Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities – net 5 1 (1 ) (1 ) — Losses on disposals 5 — (1 ) — (2 ) Other (D) (10 ) (1 ) (10 ) (1 ) (Loss) / income from operations (1 ) 69 5 149 Finance costs - net 7 (42 ) (43 ) (87 ) (89 ) Share of income of joint-ventures — — — 5 (Loss) / income before income tax (43 ) 26 (82 ) 65 Income tax benefit / (expense) 8 11 (9 ) 19 (24 ) Net (loss) / income (32 ) 17 (63 ) 41 (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, 2020 and 2019 start-up and development costs included €4 million , and €5 million , respectively, related to new projects in our AS&I operating segment. (C) For the six months ended June 30, 2019, Bowling Green one-time costs related to the acquisition included the non-cash reversal of the inventory step-up. (D) For the six months ended June 30, 2020 , Other includes €5 million of procurement penalties and termination fees incurred because of the Group's inability to fulfill certain commitments due to the Covid-19 downturn and a €5 million loss resulting from the discontinuation of hedge accounting for certain forecasted sales that were determined to be no longer expected to occur in light of the Covid-19 downturn effects.
Schedule of Segment Capital Expenditures	(in millions of Euros) Six months ended Six months ended P&ARP (38 ) (44 ) A&T (24 ) (29 ) AS&I (34 ) (56 ) Holdings & Corporate (2 ) (1 ) Capital expenditures (98 ) (130 )
Schedule of 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 1,969 1,951 A&T 818 856 AS&I 716 703 Holdings & Corporate 213 276 Segment assets 3,716 3,786 Deferred income tax assets 222 185 Cash and cash equivalents 378 184 Other financial assets 31 29 Total assets 4,347 4,184

OTHER GAINS _ (LOSSES)_NET (Tab

OTHER GAINS / (LOSSES)—NET (Tables)	6 Months Ended
	Jun. 30, 2020
Analysis of income and expense [abstract]
Schedule of Other Gains / (Losses)—Net	(in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended Realized losses on derivatives (A) (32 ) (14 ) (44 ) (28 ) Losses reclassified from OCI as a result of hedge accounting discontinuation (B) 4 (5 ) — (5 ) — Unrealized gains / (losses) on derivatives at fair value through profit and loss - net (A) 4 43 (14 ) (10 ) 17 Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities - net 4 1 (1 ) (1 ) — Losses on pension plan amendments 19 (2 ) — (2 ) — Losses on disposal 4 — (1 ) — (2 ) Other — — (1 ) (1 ) Total other gains / (losses) - net 5 (30 ) (63 ) (14 ) (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. (B) In the period ended June 30, 2020 , we determined that a portion of the hedged forecasted sales for the second half of 2020 and 2021, to which hedge accounting is applied, was no longer expected to occur. As a result, the f air value of the related derivatives accumulated in equity was reclassified in the Unaudited Interim Consolidated Income Statement and generated a €5 million loss.

CURRENCY GAINS _ (LOSSES) (Tabl

CURRENCY GAINS / (LOSSES) (Tables)	6 Months Ended
	Jun. 30, 2020
Analysis of income and expense [abstract]
Schedule 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 ended Three months ended Six months ended Six months ended Included in Revenue 18 (2 ) (1 ) (5 ) (2 ) Included in Cost of sales 1 — 1 — Included in Other gains / (losses) - net (5 ) (1 ) (6 ) 4 Total (6 ) (2 ) (10 ) 2 Realized exchange (losses) / gains on foreign currency derivatives - net 18 (3 ) — (3 ) 1 Losses reclassified from OCI as a result of hedge accounting discontinuation 18 (5 ) — (5 ) — Unrealized (losses) / gains on foreign currency derivatives - net 18 — (1 ) (2 ) 1 Exchange gains / (losses) from the remeasurement of monetary assets and liabilities - net 2 (1 ) — — Total (6 ) (2 ) (10 ) 2

FINANCE COSTS_NET (Tables)

FINANCE COSTS—NET (Tables)	6 Months Ended
	Jun. 30, 2020
Analysis of income and expense [abstract]
Schedule of Finance Costs—Net	(in millions of Euros) Three months ended Three months ended Six months ended Six months ended Interest expense on borrowings (A) (30 ) (30 ) (61 ) (62 ) Expenses on factoring arrangements (3 ) (5 ) (6 ) (10 ) Interest expense on leases (2 ) (4 ) (5 ) (7 ) Realized and unrealized (losses) / gains on debt derivatives at fair value (B) (7 ) (4 ) 1 5 Realized and unrealized exchange gains / (losses) on financing activities - net (B) 8 6 (3 ) — Interest cost on pension and other benefits (3 ) (4 ) (6 ) (8 ) Other finance expenses (6 ) (2 ) (8 ) (8 ) Capitalized borrowing costs (C) 1 — 1 1 Finance expenses (42 ) (43 ) (87 ) (89 ) Finance costs - net (42 ) (43 ) (87 ) (89 ) (A) For the six months ended June 30, 2020 , the Group incurred mainly (i) €57 million of interest related to Constellium SE Senior Notes and (ii) €3 million of interest expense and fees related to the Muscle Shoals, Bowling Green and Ravenswood ABL Facility (“Pan-U.S. ABL”). 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) €3 million of interest expense and fees related to the Pan-U.S. ABL. (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) Borrowing costs directly attributable to the construction of assets are capitalized. The capitalization rate was 6% for the six months ended June 30, 2020 and 2019 .

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings per share [abstract]
Schedule of Earnings Per Share	(in millions of Euros) Three months ended Three months ended Six months ended Six months ended Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share (33 ) 16 (64 ) 39 Number of shares attributable to equity holders of Constellium (number of shares) Three months ended Three months ended Six months ended Six months ended Weighted average number of ordinary shares used to calculate basic earnings per share 137,901,336 136,700,491 137,903,307 136,344,030 Effect of other dilutive potential ordinary shares (A) — 3,620,938 — 4,005,235 Weighted average number of ordinary shares used to calculate diluted earnings per share 137,901,336 140,321,429 137,903,307 140,349,265 (A) For the six months and three months ended June 30, 2020 , there were 4,878,787 and 4,880,758 , potential ordinary shares that could have a dilutive impact, but were considered antidilutive due to negative earnings, respectively. For the six months and three months ended June 30, 2019 , dilutive potential new ordinary shares to be issued were part of share-based compensation plans. Earnings per share attributable to the equity holders of Constellium (in Euro per share) Three months ended Three months ended Six months ended Six months ended Basic (0.24 ) 0.12 (0.46 ) 0.29 Diluted (0.24 ) 0.11 (0.46 ) 0.28

CASH AND CASH EQUIVALENTS (Tabl

CASH AND CASH EQUIVALENTS (Tables)	6 Months Ended
	Jun. 30, 2020
Cash and cash equivalents [abstract]
Schedule of Cash and Cash Equivalents	(in millions of Euros) At June 30, At December 31, Cash in bank and on hand 378 184 Total Cash and cash equivalent 378 184

TRADE RECEIVABLES AND OTHER (Ta

TRADE RECEIVABLES AND OTHER (Tables)	6 Months Ended
	Jun. 30, 2020
Trade and other receivables [abstract]
Schedule of Trade Receivables and Other	Trade receivables and other are comprised of the following: At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Trade receivables - gross — 389 — 395 Impairment — (3 ) — (2 ) Total trade receivables - net — 386 — 393 Income tax receivables 34 9 35 22 Other taxes — 17 — 35 Contract assets 31 1 16 2 Prepaid expenses 1 20 1 8 Other 8 18 8 14 Total other receivables 74 65 60 81 Total trade receivables and other 74 451 60 474
Schedule of Contract Assets	At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Unbilled tooling costs 14 — 16 — Other 17 1 — 2 Total Contract assets 31 1 16 2
Schedule of Aging of Total Trade Receivables—Net	The aging of total trade receivables - net is as follows: (in millions of Euros) At June 30, At December 31, Not past due 369 380 1 – 30 days past due 15 10 31 – 60 days past due 2 3 61 – 90 days past due — — Greater than 90 days past due — — Total trade receivables - net 386 393
Schedule 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: (in millions of Euros) At June 30, At December 31, Euro 158 126 U.S. Dollar 203 251 Swiss franc 14 3 Other currencies 11 13 Total trade receivables - net 386 393

INVENTORIES (Tables)

INVENTORIES (Tables)	6 Months Ended
	Jun. 30, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of Inventories	(in millions of Euros) At June 30, At December 31, Finished goods 194 203 Work in progress 303 321 Raw materials 99 106 Stores and supplies 77 74 Inventories write-down (38 ) (34 ) Total inventories 635 670

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	6 Months Ended
	Jun. 30, 2020
Property, plant and equipment [abstract]
Schedule of Property, Plant and Equipment	(in millions of Euros) Land and Property Rights Buildings Machinery and Equipment Construction Work in Progress Other Total Net balance at January 1, 2020 19 366 1,451 203 17 2,056 Additions — 9 36 66 1 112 Disposals — — (2 ) — — (2 ) Depreciation and impairment — (14 ) (108 ) (5 ) (5 ) (132 ) Transfer during the year 2 18 52 (74 ) 2 — Effects of changes in foreign exchange rates — (1 ) — (2 ) — (3 ) Net balance at June 30, 2020 21 378 1,429 188 15 2,031 Cost 37 552 2,488 198 47 3,322 Less accumulated depreciation and impairment (16 ) (174 ) (1,059 ) (10 ) (32 ) (1,291 ) Net balance at June 30, 2020 21 378 1,429 188 15 2,031
Schedule of Right of Use Assets Included in Property, Plant and Equipment	Right of use have been included within the same line item as that within which the corresponding underlying assets would be presented if they were owned. (in millions of Euros) Buildings Machinery and Equipment Other Total Net balance at January 1, 2020 116 71 3 190 Additions 9 10 1 20 Disposals (1 ) — — (1 ) Depreciation (6 ) (11 ) (1 ) (18 ) Effects of changes in foreign exchange rates — (1 ) — (1 ) Net balance at June 30, 2020 118 69 3 190 Cost 142 121 5 268 Less accumulated depreciation and impairment (24 ) (52 ) (2 ) (78 ) Net balance at June 30, 2020 118 69 3 190

INTANGIBLE ASSETS (INCLUDING _2

INTANGIBLE ASSETS (INCLUDING GOODWILL) (Tables)	6 Months Ended
	Jun. 30, 2020
Intangible assets and goodwill [abstract]
Schedule of Changes in Intangible Assets and Goodwill	(in millions of Euros) Goodwill Technology Computer Software Customer relationships Work in Progress Other Total intangible assets (excluding goodwill) Net balance at January 1, 2020 455 21 19 14 14 2 70 Additions — — — — 3 — 3 Amortization expense — (1 ) (4 ) — — — (5 ) Transfer during the year — — 1 — (1 ) — — Effects of changes in foreign exchange rates 1 — — — — — — Net balance at June 30, 2020 456 20 16 14 16 2 68 Cost 456 86 75 40 17 2 220 Less accumulated depreciation and impairment — (66 ) (59 ) (26 ) (1 ) — (152 ) Net balance at June 30, 2020 456 20 16 14 16 2 68

TRADE PAYABLES AND OTHER (Table

TRADE PAYABLES AND OTHER (Tables)	6 Months Ended
	Jun. 30, 2020
Trade and other payables [abstract]
Schedule of Trade Payables and Other	At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Trade payables — 683 — 711 Fixed assets payables — 29 — 43 Employees' entitlements — 173 — 171 Taxes payable other than income tax — 33 — 14 Contract liabilities and other liabilities to customers 5 78 6 54 Other payables 14 7 15 6 Total other 19 320 21 288 Total trade payables and other 19 1,003 21 999
Schedule of Contract Liabilities	At June 30, At December 31, (in millions of Euros) Non-current Current Non-current Current Deferred tooling revenue 2 — 2 — Advance payment from customers 1 4 2 5 Unrecognized variable consideration (A) 2 57 2 46 Other — 17 — 3 Total contract liabilities and other liabilities to customers 5 78 6 54 (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, 2020
Borrowings [abstract]
Schedule of Borrowings by Nature	(in millions of Euros) At June 30, At December 31, Nominal Value in Currency Nominal rate Effective rate Nominal Value In Euros (Arrangement fees) Accrued interests Carrying value Carrying value Secured Pan-U.S. ABL $ — Floating 3.43 % — — — — 127 Secured U.S. DDTL $ — Floating — — — — — — Secured French Loan € 180 Floating 2.50 % 180 — — 180 — Secured Inventory Based Facility (due 2021) — Floating — — — — — — Senior Unsecured Notes Constellium SE $ 400 5.75 % 6.26 % 357 (3 ) 3 357 355 Constellium SE € — 4.63 % 5.16 % — — — — 200 Constellium SE $ 650 6.63 % 7.13 % 580 (9 ) 13 584 582 Constellium SE $ 500 5.88 % 6.26 % 447 (6 ) 10 451 449 Constellium SE € 400 4.25 % 4.57 % 400 (5 ) 6 401 400 Constellium SE $ 325 5.63 % 6.05 % 290 (6 ) — 284 — Unsecured Revolving Credit Facility (due 2021) (D) — Floating — — — — — — Unsecured Credit facility Switzerland (due 2025) (E) CHF 20 1.18 % 1.18 % 18 — — 18 — Lease liabilities 190 — 1 191 188 Other loans (F) 68 — 2 70 60 Total Borrowings 2,530 (29 ) 35 2,536 2,361 Of which non-current 2,434 2,160 Of which current 102 201 Constellium SE Senior Notes are guaranteed by certain subsidiaries. (A) On April 24, 2020, Constellium Muscle Shoals, Constellium Rolled Product Ravenswood, LLC and Constellium Bowling Green amended the Pan-U.S. ABL to include a delay-draw term loan (the “ U.S. DDTL ” ) of $166 million . (B) On May 13, 2020, one of our French entities entered into a term facility agreement with a syndicate of banks (the “French Loan”), 80% guaranteed by the French State. The French Loan established a fully committed term loan for an aggregate amount up to €180 million , of which €30 million was provided by Bpifrance Financement, a related party. The French Loan will mature no earlier than May 20, 2021, and the Company has the option to extend it for up to five years . (C) On June 30, 2020, Constellium SE issued $325 million principal amount of the 5.625% Senior Notes due 2028. Deferred arrangement fees amounted to €6 million on the issuance date. A portion of the net proceeds from the issuance were used to repurchase the remaining €200 million of the 4.625% Constellium SE Senior Unsecured Notes issued in May 2014, due 2021. (D) The Unsecured Revolving Credit Facility has a €5 million borrowing base and is provided by Bpifrance Financement, a related party. (E) On May 22, 2020, Constellium Valais entered into an uncommitted revolving credit facility for an amount of CHF 20 million , 85% guaranteed by the Swiss state. This facility may be terminated by either party at any time. (F) Other loans include €38 million of financial liabilities relating to the sale and leaseback of assets that were considered to be financing arrangements in substance.
Schedule of Movement in Borrowings	(in millions of Euros) Six months ended Year ended December 31,2019 At December 31, prior year 2,361 2,151 IFRS 16 application — 102 At January 1 2,361 2,253 Cash flows Proceeds from issuance of Senior Notes (A) 290 — Repayment of Senior Notes (B) (200 ) (100 ) Proceeds from French loan 180 — Proceeds from Swiss credit facility 18 — (Repayments) / proceeds from U.S. revolving credit facility and other loans (124 ) 109 Payment of deferred financing costs (6 ) — Lease repayments (17 ) (86 ) Non-cash changes Borrowings assumed through business combination — 75 Movement in interests accrued or capitalized (1 ) 1 New leases and other loans 25 75 Deferred arrangement fees and other 3 5 Effects of changes in foreign exchange rates 7 29 At the end of the period 2,536 2,361 (A) The proceeds from the Senior Notes issued on June 30, 2020 were €290 million , converted at the issuance date exchange rate of EUR/USD= 1.1198 . (B) On June 30, 2020, the remaining €200 million of the 4.625% Senior Notes due 2021 were redeemed. On August 8, 2019, €100 million of the €300 million outstanding aggregate principal amount of the 4.625% Senior Notes due 2021 were redeemed.
Schedule of Currency Concentration 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 1,757 1,597 Euro 741 746 Other currencies 38 18 Total borrowings 2,536 2,361

FINANCIAL INSTRUMENTS (Tables)

FINANCIAL INSTRUMENTS (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of detailed information about financial instruments [abstract]
Schedule of Financial Assets and Liabilities by Categories	At June 30, At December 31, (in millions of Euros) Notes At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total Cash and cash equivalents 10 378 — — 378 184 — — 184 Trade receivables 11 — — 386 386 — — 393 393 Other financial assets — 31 — 31 — 29 — 29 Total 378 31 386 795 184 29 393 606 At June 30, At December 31, (in millions of Euros) Notes At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total Trade payables and fixed assets payables 15 712 — — 712 754 — — 754 Borrowings 16 2,536 — — 2,536 2,361 — — 2,361 Other financial liabilities — 61 14 75 — 44 14 58 Total 3,248 61 14 3,323 3,115 44 14 3,173
Schedule of Other Financial Assets and Other Financial Liabilities Positions	At June 30, At December 31, (in millions of Euros) Notes At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total At amortized cost At Fair Value through Profit and loss At Fair Value through OCI Total Trade payables and fixed assets payables 15 712 — — 712 754 — — 754 Borrowings 16 2,536 — — 2,536 2,361 — — 2,361 Other financial liabilities — 61 14 75 — 44 14 58 Total 3,248 61 14 3,323 3,115 44 14 3,173 The table below details other financial assets and other financial liabilities positions: At June 30, At December 31, (in millions of Euros) Non-current Current Total Non-current Current Total Derivatives 9 22 31 7 22 29 Aluminium and premium future contracts 2 11 13 1 8 9 Energy future contracts — — — — — — Other future contracts — — — — — — Currency commercial contracts 7 10 17 5 12 17 Currency net debt derivatives — 1 1 1 2 3 Other financial assets 9 22 31 7 22 29 Derivatives 30 45 75 23 35 58 Aluminium and premium future contracts 9 19 28 4 10 14 Energy future contracts — — — — 1 1 Other future contracts 1 4 5 2 4 6 Currency commercial contracts 15 21 36 12 16 28 Currency net debt derivatives 5 1 6 5 4 9 Other financial liabilities 30 45 75 23 35 58
Schedule of Derivatives Measured at Fair Value	At June 30, At December 31, (in millions of Euros) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Other financial assets - derivatives 12 19 — 31 8 21 — 29 Other financial liabilities - derivatives 30 45 — 75 19 39 — 58

FINANCIAL RISK MANAGEMENT (Tabl

FINANCIAL RISK MANAGEMENT (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of financial risk management [Abstract]
Schedule 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 Consolidated Income Statement and the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss): (in millions of Euros) Notes Three months ended Three months ended Six months ended Six months ended Derivatives that do not qualify for hedge accounting Included in Other gains / (losses) - net Realized gains on foreign currency derivatives - net 6 — 1 2 3 Unrealized (losses) / gains on foreign currency derivatives - net (A) 6 (1 ) (1 ) (2 ) 1 Derivatives that qualify for hedge accounting Included in Revenue Realized losses on foreign currency derivatives - net 6 (3 ) (1 ) (5 ) (2 ) Unrealized gains on foreign currency derivatives - net 6 1 — — — Included in Other gains / (losses) - net Losses reclassified from OCI as a result of hedge accounting discontinuation (B) 6 (5 ) — (5 ) — Included in Other comprehensive income / (loss) — Unrealized gains / (losses) on foreign currency derivatives - net 2 1 (6 ) (7 ) Gains reclassified from cash flow hedge reserve to the Unaudited Interim Consolidated Income Statement 3 1 6 2 (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 years when these sales are recognized. (B) In the period ended June 30, 2020 , we determined that a portion of the hedged forecasted sales for the second half of 2020 and 2021, to which hedge accounting is applied, was no longer expected to occur. As a result, the f air value of the related derivatives accumulated in equity was reclassified in the Unaudited Interim Consolidated Income Statement and generated a €5 million loss.

PENSIONS AND OTHER POST-EMPLO_2

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of employee benefits [Abstract]
Schedule of Actuarial Assumptions	Pension and other post-employment benefit obligations were updated based on the discount rates applicable at June 30, 2020 . At June 30, At December 31, Switzerland 0.20% 0.15% US Hourly pension 2.70% - 2.85% 3.15% - 3.25% Salaried pension 2.75% 3.25% OPEB 2.70% - 3.00% 3.20% - 3.40% Other benefits 2.45% - 2.75% 3.00% - 3.20% France Retirements 0.95% 0.95% Other benefits 0.85% 0.80% Germany 1.05% 1.00%
Schedule of the Consolidated Statement of Financial Position	At June 30, At December 31, (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Present value of funded obligation 789 — 789 768 — 768 Fair value of plan assets (435 ) — (435 ) (445 ) — (445 ) Deficit of funded plans 354 — 354 323 — 323 Present value of unfunded obligation 131 230 361 127 220 347 Net liability arising from defined benefit obligation 485 230 715 450 220 670
Schedule of Amounts Recognised In Unaudited Interim Income Statement	Three months ended Three months ended (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Service cost Current service cost (5 ) (1 ) (6 ) (5 ) (1 ) (6 ) Past service cost — (2 ) (2 ) — — — Net interest (2 ) (1 ) (3 ) (2 ) (2 ) (4 ) Immediate recognition of gains / (losses) arising over the period — (1 ) (1 ) — (2 ) (2 ) Administration expenses (1 ) — (1 ) — — — Total (8 ) (5 ) (13 ) (7 ) (5 ) (12 ) Six months ended Six months ended (in millions of Euros) Pension Benefits Other Benefits Total Pension Benefits Other Benefits Total Service cost Current service cost (11 ) (3 ) (14 ) (9 ) (3 ) (12 ) Past service cost — (2 ) (2 ) — — — Net interest (3 ) (3 ) (6 ) (4 ) (4 ) (8 ) Immediate recognition of gains / (losses) arising over the period — — — — (2 ) (2 ) Administration expenses (1 ) — (1 ) (1 ) — (1 ) Total (15 ) (8 ) (23 ) (14 ) (9 ) (23 )
Schedule of Movement in Net Defined Benefit Obligations	At June 30, Defined benefit obligations Plan Assets Net defined benefit liability (in millions of Euros) Pension benefits Other benefits Total At January 1, 2020 895 220 1,115 (445 ) 670 Included in the Unaudited Interim Consolidated Income Statement Current service cost 11 3 14 — 14 Interest cost / (income) 7 3 10 (4 ) 6 Past service cost — 2 2 — 2 Immediate recognition of gains / (losses) arising over the year — — — — — Administration expenses — — — 1 1 Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss) Remeasurements due to: —actual return less interest on plan assets — — — 13 13 —changes in financial assumptions 16 11 27 — 27 —changes in demographic assumptions — — — — — —experience losses 1 (1 ) — — — Effects of changes in foreign exchange rates 6 1 7 (5 ) 2 Included in the Unaudited Interim Consolidated Statement of Cash Flows Benefits paid (18 ) (9 ) (27 ) 17 (10 ) Contributions by the Group — — — (10 ) (10 ) Contributions by the plan participants 2 — 2 (2 ) — At June 30, 2020 920 230 1,150 (435 ) 715
Schedule of Net Defined Benefit Obligations by Country	At June 30, At December 31, (in millions of Euros) Defined benefit obligations Plan assets Net defined benefit liability Defined benefit obligations Plan assets Net defined benefit liability France 164 (3 ) 161 161 (3 ) 158 Germany 140 (1 ) 139 144 (1 ) 143 Switzerland 303 (213 ) 90 299 (214 ) 85 United States 542 (218 ) 324 510 (227 ) 283 Other countries 1 — 1 1 — 1 Total 1,150 (435 ) 715 1,115 (445 ) 670

PROVISIONS (Tables)

PROVISIONS (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of other provisions [abstract]
Schedule of Changes in Provisions	(in millions of Euros) Notes Close down and environmental remediation costs Restructuring Legal claims Total At January 1, 2020 90 4 28 122 Allowance — 11 2 13 Amounts used — (5 ) — (5 ) Unused amounts reversed — — (4 ) (4 ) Unwinding of discounts 1 — — 1 Effects of changes in foreign exchange rates 1 — — 1 At June 30, 2020 92 10 26 128 Current 7 9 13 29 Non-Current 85 1 13 99 Total Provisions 92 10 26 128
Schedule of Legal Claims and Other Costs	(in millions of Euros) At June 30, At December 31, Litigation 19 21 Disease claims 4 4 Other 3 3 Total Provisions for legal claims and other costs 26 28

SHARE CAPITAL (Tables)

SHARE CAPITAL (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of share capital, reserves and other equity interest [Abstract]
Schedule of Share Capital	(in millions of Euros) Number of shares Share capital Share premium At January 1, 2020 137,867,418 3 420 New shares issued 54,614 — — At June 30, 2020 137,922,032 3 420

SHARE-BASED COMPENSATION (Table

SHARE-BASED COMPENSATION (Tables)	6 Months Ended
	Jun. 30, 2020
Share-based payment arrangements [Abstract]
Schedule of Inputs to the Model Used for PSUs Granted	The following table lists the inputs to the model used for the PSUs granted in April 2020: Six months ended Fair value at grant date (in euros) 6.65 Share price at grant date (in euros) 4.64 Dividend yield — Expected volatility (A) 63 % Risk-free interest rate (US government bond yield) 0.36 % Model used Monte Carlo
Schedule of Number and Movement of Potential Shares	he following table illustrates the number and movements in potential shares: Performance Share Units (PSUs) Restricted Stock Units (RSUs) Equity Award Plans Total Potential Shares At December 31, 2019 2,519,294 2,066,503 79,526 4,665,323 Granted (A) 1,049,839 910,047 — 1,959,886 Vested — (8,000 ) (46,614 ) (54,614 ) Forfeited (B) (46,306 ) (50,931 ) — (97,237 ) At June 30, 2020 3,522,827 2,917,619 32,912 6,473,358 (A) For PSUs, the number of potential shares granted is presented using a vesting multiplier of 100% . (B) For potential shares related to PSUs, 46,306 were forfeited following the departure of certain beneficiaries and none were forfeited in relation to the non-fulfilment of performance conditions.

GENERAL INFORMATION (Details)

GENERAL INFORMATION (Details)	Jun. 30, 2020EmployeesCenterFacilitysite
Disclosure of general information [abstract]
Number of production facilities | Facility	28
Number of administrative and commercial sites | site	3
Number of R&D centers | Center	3
Number of employees | Employees	12,400

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Disclosure of Foreign Exchange Rates (Details)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disclosure of foreign exchange rates [line items]
Closing rate	1.1198
U.S. Dollars
Disclosure of foreign exchange rates [line items]
Average rate	1.1018	1.1297
Closing rate	1.1198		1.1234
Swiss Francs
Disclosure of foreign exchange rates [line items]
Average rate	1.0641	1.1294
Closing rate	1.0651		1.0854
Czech Koruna
Disclosure of foreign exchange rates [line items]
Average rate	26.2970	25.6842
Closing rate	26.7400		25.4080

REVENUE - Disaggregation of Rev

REVENUE - Disaggregation of Revenue by Product Line (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disclosure of products and services [line items]
Total Revenue	€ 1,031	€ 1,538	€ 2,468	€ 3,074
Packaging rolled products
Disclosure of products and services [line items]
Total Revenue	456	568	980	1,116
Automotive rolled products
Disclosure of products and services [line items]
Total Revenue	88	209	281	439
Specialty and other thin-rolled products
Disclosure of products and services [line items]
Total Revenue	20	42	52	90
Aerospace rolled products
Disclosure of products and services [line items]
Total Revenue	142	224	365	429
Transportation, Industry and other rolled products
Disclosure of products and services [line items]
Total Revenue	105	148	231	310
Automotive extruded products
Disclosure of products and services [line items]
Total Revenue	96	199	295	387
Other extruded products
Disclosure of products and services [line items]
Total Revenue	€ 124	€ 148	€ 264	€ 303

REVENUE - Disaggregation of R_2

REVENUE - Disaggregation of Revenue by Destination of Shipment (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disclosure of geographical areas [line items]
Total Revenue	€ 1,031	€ 1,538	€ 2,468	€ 3,074
France
Disclosure of geographical areas [line items]
Total Revenue	67	154	188	306
Germany
Disclosure of geographical areas [line items]
Total Revenue	192	339	479	678
United Kingdom
Disclosure of geographical areas [line items]
Total Revenue	39	49	108	99
Switzerland
Disclosure of geographical areas [line items]
Total Revenue	15	18	27	38
Other Europe
Disclosure of geographical areas [line items]
Total Revenue	201	286	476	555
United States
Disclosure of geographical areas [line items]
Total Revenue	413	600	974	1,164
United States
Disclosure of geographical areas [line items]
Total Revenue	7	9	24	27
Asia and Other Pacific
Disclosure of geographical areas [line items]
Total Revenue	61	68	118	137
All Other
Disclosure of geographical areas [line items]
Total Revenue	€ 36	€ 15	€ 74	€ 70

REVENUE - Additional Informatio

REVENUE - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020
Performance obligations satisfied over time
Disclosure of geographical areas [line items]
Percentage of payment option over total revenue	1.00%

OPERATING SEGMENT INFORMATION -

OPERATING SEGMENT INFORMATION - Additional Information (Details) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020EUR (€)Employees	Jun. 30, 2019EUR (€)	Jun. 30, 2020EUR (€)Employees	Jun. 30, 2019EUR (€)
Disclosure of operating segments [line items]
Number of employees | Employees	12,400		12,400
Revenue	€ 1,031	€ 1,538	€ 2,468	€ 3,074
P&ARP
Disclosure of operating segments [line items]
Revenue	564	819	1,313	1,645
A&T
Disclosure of operating segments [line items]
Revenue	247	372	596	739
AS&I
Disclosure of operating segments [line items]
Revenue	€ 220	€ 347	€ 559	€ 690

OPERATING SEGMENT INFORMATION_2

OPERATING SEGMENT INFORMATION - Segment Revenue (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disclosure of operating segments [line items]
Revenue	€ 1,031	€ 1,538	€ 2,468	€ 3,074
P&ARP
Disclosure of operating segments [line items]
Revenue	564	819	1,313	1,645
A&T
Disclosure of operating segments [line items]
Revenue	247	372	596	739
AS&I
Disclosure of operating segments [line items]
Revenue	220	347	559	690
Holdings & Corporate
Disclosure of operating segments [line items]
Revenue	0	0	0	0
Segment revenue
Disclosure of operating segments [line items]
Revenue	1,037	1,551	2,490	3,101
Segment revenue | P&ARP
Disclosure of operating segments [line items]
Revenue	565	821	1,317	1,649
Segment revenue | A&T
Disclosure of operating segments [line items]
Revenue	250	383	609	761
Segment revenue | AS&I
Disclosure of operating segments [line items]
Revenue	222	347	564	691
Segment revenue | Holdings & Corporate
Disclosure of operating segments [line items]
Revenue	0	0	0	0
Inter-segment elimination
Disclosure of operating segments [line items]
Revenue	(6)	(13)	(22)	(27)
Inter-segment elimination | P&ARP
Disclosure of operating segments [line items]
Revenue	(1)	(2)	(4)	(4)
Inter-segment elimination | A&T
Disclosure of operating segments [line items]
Revenue	(3)	(11)	(13)	(22)
Inter-segment elimination | AS&I
Disclosure of operating segments [line items]
Revenue	(2)	0	(5)	(1)
Inter-segment elimination | Holdings & Corporate
Disclosure of operating segments [line items]
Revenue	€ 0	€ 0	€ 0	€ 0

OPERATING SEGMENT INFORMATION_3

OPERATING SEGMENT INFORMATION - Segment Adjusted EBITDA and reconciliation of Adjusted EBITDA to Net Income (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	€ 81	€ 167	€ 228	€ 302
Metal price lag	(25)	(13)	(40)	(31)
Start-up and development costs	(2)	(3)	(4)	(5)
Bowling Green one-time costs related to the acquisition	0	0	0	(6)
Share-based compensation costs	(5)	(4)	(8)	(7)
Gains on pension plan amendments	(2)	0	(2)	0	€ 0
Depreciation, amortization and impairment	(71)	(60)	(137)	(117)
Restructuring costs	(11)	(1)	(11)	(1)
Unrealized gains / (losses) on derivatives	43	(14)	(10)	17
Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities – net	1	(1)	(1)	0
(Losses) / gains on disposals	0	(1)	0	(2)
Other	(10)	(1)	(10)	(1)
(Loss) / income from operations	(1)	69	5	149
Finance costs - net	(42)	(43)	(87)	(89)
Share of income of joint-ventures	0	0	0	5
(Loss) / income before income tax	(43)	26	(82)	65
Income tax benefit / (expense)	11	(9)	19	(24)
Net (loss) / income	(32)	17	(63)	41	€ 64
Procurement penalties and termination fees			5
Loss on hedge ineffectiveness recognised in profit or loss	5	0	5	0
P&ARP
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	58	79	124	138
A&T
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	31	64	83	116
AS&I
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	(1)	30	33	59
Start-up and development costs			(4)	(5)
Holdings & Corporate
Disclosure of segment adjusted EBITDA and reconciliation of adjusted EBITDA to net income [line items]
Adjusted EBITDA	€ (7)	€ (6)	€ (12)	€ (11)

OPERATING SEGMENT INFORMATION_4

OPERATING SEGMENT INFORMATION - Segment Capital Expenditures (Details) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of operating segments [line items]
Capital expenditures	€ (98)	€ (130)
P&ARP
Disclosure of operating segments [line items]
Capital expenditures	(38)	(44)
A&T
Disclosure of operating segments [line items]
Capital expenditures	(24)	(29)
AS&I
Disclosure of operating segments [line items]
Capital expenditures	(34)	(56)
Holdings & Corporate
Disclosure of operating segments [line items]
Capital expenditures	€ (2)	€ (1)

OPERATING SEGMENT INFORMATION_5

OPERATING SEGMENT INFORMATION - Segment Assets (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Disclosure of operating segments [line items]
Total Assets	€ 4,347	€ 4,184
Deferred income tax assets	222	185
Cash and cash equivalents	378	184	€ 213	€ 164
Other financial assets	31	29
Segment revenue
Disclosure of operating segments [line items]
Total Assets	3,716	3,786
Segment revenue | P&ARP
Disclosure of operating segments [line items]
Total Assets	1,969	1,951
Segment revenue | A&T
Disclosure of operating segments [line items]
Total Assets	818	856
Segment revenue | AS&I
Disclosure of operating segments [line items]
Total Assets	716	703
Segment revenue | Holdings & Corporate
Disclosure of operating segments [line items]
Total Assets	213	276
Unallocated
Disclosure of operating segments [line items]
Deferred income tax assets	222	185
Cash and cash equivalents	378	184
Other financial assets	€ 31	€ 29

OTHER GAINS _ (LOSSES)_NET (Det

OTHER GAINS / (LOSSES)—NET (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Analysis of income and expense [abstract]
Realized (losses) / gains on derivatives	€ (32)	€ (14)	€ (44)	€ (28)
Losses reclassified from OCI as a result of hedge accounting discontinuation	(5)	0	(5)	0
Unrealized gains / (losses) on derivatives at fair value through profit and loss—net	43	(14)	(10)	17
Unrealized exchange gains / (losses) from the remeasurement of monetary assets and liabilities – net	1	(1)	(1)	0
Gains on pension plan amendments	(2)	0	(2)	0	€ 0
(Losses) / gains on disposals	0	(1)	0	(2)
Other	0	0	(1)	(1)
Total other gains / (losses) - net	€ 5	€ (30)	€ (63)	€ (14)

CURRENCY GAINS _ (LOSSES) - Cur

CURRENCY GAINS / (LOSSES) - Currency Gains and Losses Included in Income from Operations (Details) € in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020EUR (€)	Jun. 30, 2020USD ($)	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2020EUR (€)	Jun. 30, 2020USD ($)	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)
Analysis of income and expense [line items]
Total currency gains / (losses) - net	€ (6)	$ (6)	€ (2)	$ (2)	€ (10)	$ (10)	€ 2	$ 2
Realized exchange (losses) / gains on foreign currency derivatives - net	(3)		0		(3)		1
Gain (loss) on hedge ineffectiveness recognised in profit or loss	(5)		0		(5)		0
Unrealized (losses) / gains on foreign currency derivatives - net	0		(1)		(2)		1
Exchange gains / (losses) from the remeasurement of monetary assets and liabilities - net	2		(1)		0		0
Included in Revenue
Analysis of income and expense [line items]
Total currency gains / (losses) - net	(2)		(1)		(5)		(2)
Included in Cost of sales
Analysis of income and expense [line items]
Total currency gains / (losses) - net	1		0		1		0
Included in Other gains / (losses) - net
Analysis of income and expense [line items]
Total currency gains / (losses) - net	€ (5)		€ (1)		€ (6)		€ 4

FINANCE COSTS_NET (Details)

FINANCE COSTS—NET (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Analysis of income and expense [line items]
Interest expense on borrowings	€ (30)	€ (30)	€ (61)	€ (62)
Expenses on factoring arrangements	(3)	(5)	(6)	(10)
Interest expense on leases	(2)	(4)	(5)	(7)
Realized and unrealized (losses) / gains on debt derivatives at fair value	(7)	(4)	1	5
Realized and unrealized exchange (losses) / gains on financing activities - net	8	6	(3)	0
Interest cost on pension and other benefits	(3)	(4)	(6)	(8)
Other finance expenses	(6)	(2)	(8)	(8)
Capitalized borrowing costs	1	0	1	1
Finance expenses	(42)	(43)	(87)	(89)
Finance costs - net	€ (42)	€ (43)	€ (87)	€ (89)
Capitalization rate			6.00%	6.00%
Constellium SE Senior Notes
Analysis of income and expense [line items]
Interest expense on debt instruments issued			€ 57	€ 58
Pan US ABL Facility
Analysis of income and expense [line items]
Interest expense on debt instruments issued			€ 3	€ 3

EARNINGS PER SHARE - Earnings A

EARNINGS PER SHARE - Earnings Attributable to Equity Holders of Parent used to Calculate Basic and Diluted Earnings per share (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings per share [abstract]
Earnings attributable to equity holders of the parent used to calculate basic and diluted earnings per share	€ (33)	€ 16	€ (64)	€ 39

EARNINGS PER SHARE - Number of

EARNINGS PER SHARE - Number of Shares Attributable to Equity Holders (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings per share [abstract]
Weighted average number of ordinary shares used to calculate basic earnings per share (in shares)	137,901,336	136,700,491	137,903,307	136,344,030
Effect of other dilutive potential ordinary shares (in shares)	0	3,620,938	0	4,005,235
Weighted average number of ordinary shares used to calculate diluted earnings per share (in shares)	137,901,336	140,321,429	137,903,307	140,349,265
Potential ordinary shares (in shares)	4,880,758		4,878,787

EARNINGS PER SHARE - Earnings P

EARNINGS PER SHARE - Earnings Per Share Attributable to the Equity Holders (Details) - € / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings per share [abstract]
Basic (in EUR per share)	€ (0.24)	€ 0.12	€ (0.46)	€ 0.29
Diluted (in EUR per share)	€ (0.24)	€ 0.11	€ (0.46)	€ 0.28

CASH AND CASH EQUIVALENTS (Deta

CASH AND CASH EQUIVALENTS (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash and cash equivalents [abstract]
Cash in bank and on hand	€ 378	€ 184
Total Cash and cash equivalent	€ 378	€ 184	€ 213	€ 164

CASH AND CASH EQUIVALENTS - Add

CASH AND CASH EQUIVALENTS - Additional Information (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of cash and cash equivalents [line Items]
Cash in bank and on hand	€ 378	€ 184
Subsidiaries in capital control restrictions countries
Disclosure of cash and cash equivalents [line Items]
Cash in bank and on hand	€ 22	€ 22

TRADE RECEIVABLES AND OTHER (De

TRADE RECEIVABLES AND OTHER (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Non-current
Trade receivables	€ 0	€ 0
Income tax receivables	34	35
Other taxes	0	0
Contract assets	31	16
Prepaid expenses	1	1
Other	8	8
Total other receivables	74	60
Total trade receivables and other	74	60
Current
Trade receivables	386	393
Income tax receivables	9	22
Other taxes	17	35
Contract assets	1	2
Prepaid expenses	20	8
Other	18	14
Total other receivables	65	81
Total trade receivables and other	451	474
Cost
Non-current
Trade receivables	0	0
Current
Trade receivables	389	395
Impairment
Non-current
Trade receivables	0	0
Current
Trade receivables	€ (3)	€ (2)

TRADE RECEIVABLES AND OTHER - C

TRADE RECEIVABLES AND OTHER - Contract Assets (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contact assets, Non-current	€ 31	€ 16
Contract assets, Current	1	2
Unbilled tooling costs
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contact assets, Non-current	14	16
Contract assets, Current	0	0
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contact assets, Non-current	17	0
Contract assets, Current	€ 1	€ 2

TRADE RECEIVABLES AND OTHER - A

TRADE RECEIVABLES AND OTHER - Aging of Total Trade Receivables - Net (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Trade receivables [line items]
Trade receivables	€ 386	€ 393
Not past due
Trade receivables [line items]
Trade receivables	369	380
1 – 30 days past due
Trade receivables [line items]
Trade receivables	15	10
31 – 60 days past due
Trade receivables [line items]
Trade receivables	2	3
61 – 90 days past due
Trade receivables [line items]
Trade receivables	0	0
Greater than 90 days past due
Trade receivables [line items]
Trade receivables	€ 0	€ 0

TRADE RECEIVABLES AND OTHER -_2

TRADE RECEIVABLES AND OTHER - Additional Information (Details)	Dec. 09, 2019USD ($)	Sep. 29, 2019USD ($)	Jun. 30, 2020EUR (€)	Jun. 30, 2019EUR (€)	Dec. 31, 2019EUR (€)
Disclosure of trade and other receivables [line items]
Allowance recognized for impairment on trade receivables			€ 400,000	€ 100,000
Factored assets			506,000,000		€ 574,000,000
Factored assets, derecognized from Consolidated Statement of Financial Position			(390,000,000)		463,000,000
Factored assets, recognized in Consolidated Statement of Financial Position			116,000,000		111,000,000
Debt due factor			6,839,649		€ 0
Factoring of receivables | Muscle Shoals factoring facility
Disclosure of trade and other receivables [line items]
Factoring maximum capacity | $		$ 300,000,000
France | Factoring of receivables
Disclosure of trade and other receivables [line items]
Factoring maximum capacity			255,000,000
Germany, Switzerland and Czech Republic | Factoring of receivables
Disclosure of trade and other receivables [line items]
Factoring maximum capacity			€ 150,000,000
United States | Factoring of receivables | Constellium automotive
Disclosure of trade and other receivables [line items]
Factoring maximum capacity | $	$ 25,000,000

TRADE RECEIVABLES AND OTHER -_3

TRADE RECEIVABLES AND OTHER - Carrying Amounts of Total Trade Receivables - Net by Currency (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Trade receivables [line items]
Trade receivables	€ 386	€ 393
Euro
Trade receivables [line items]
Trade receivables	158	126
U.S. Dollars
Trade receivables [line items]
Trade receivables	203	251
Swiss Francs
Trade receivables [line items]
Trade receivables	14	3
Other currencies
Trade receivables [line items]
Trade receivables	€ 11	€ 13

INVENTORIES (Details)

INVENTORIES (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Finished goods	€ 194	€ 203
Work in progress	303	321
Raw materials	99	106
Stores and supplies	77	74
Inventories write-down	(38)	(34)
Total inventories	€ 635	€ 670

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	€ 2,056
Additions	112
Disposals	(2)
Depreciation and impairment	(132)
Transfer during the year	0
Effects of changes in foreign exchange rates	(3)
Ending balance	2,031
Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	3,322
Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(1,291)
Land and Property Rights
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	19
Additions	0
Disposals	0
Depreciation and impairment	0
Transfer during the year	2
Effects of changes in foreign exchange rates	0
Ending balance	21
Land and Property Rights | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	37
Land and Property Rights | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(16)
Buildings
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	366
Additions	9
Disposals	0
Depreciation and impairment	(14)
Transfer during the year	18
Effects of changes in foreign exchange rates	(1)
Ending balance	378
Buildings | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	552
Buildings | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(174)
Machinery and Equipment
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	1,451
Additions	36
Disposals	(2)
Depreciation and impairment	(108)
Transfer during the year	52
Effects of changes in foreign exchange rates	0
Ending balance	1,429
Machinery and Equipment | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	2,488
Machinery and Equipment | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(1,059)
Construction Work in Progress
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	203
Additions	66
Disposals	0
Depreciation and impairment	(5)
Transfer during the year	(74)
Effects of changes in foreign exchange rates	(2)
Ending balance	188
Construction Work in Progress | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	198
Construction Work in Progress | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(10)
Other
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	17
Additions	1
Disposals	0
Depreciation and impairment	(5)
Transfer during the year	2
Effects of changes in foreign exchange rates	0
Ending balance	15
Other | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	47
Other | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	€ (32)

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Right of Use Assets Included in Property, Plant and Equipment (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	€ 2,056
Additions	112
Disposals	(2)
Depreciation and impairment	(132)
Effects of changes in foreign exchange rates	(3)
Ending balance	2,031
Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	3,322
Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(1,291)
Buildings
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	366
Additions	9
Disposals	0
Depreciation and impairment	(14)
Effects of changes in foreign exchange rates	(1)
Ending balance	378
Buildings | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	552
Buildings | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(174)
Machinery and Equipment
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	1,451
Additions	36
Disposals	(2)
Depreciation and impairment	(108)
Effects of changes in foreign exchange rates	0
Ending balance	1,429
Machinery and Equipment | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	2,488
Machinery and Equipment | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(1,059)
Other
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	17
Additions	1
Disposals	0
Depreciation and impairment	(5)
Effects of changes in foreign exchange rates	0
Ending balance	15
Other | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	47
Other | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(32)
Right-of-use assets
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	190
Additions	20
Disposals	(1)
Depreciation and impairment	(18)
Effects of changes in foreign exchange rates	(1)
Ending balance	190
Right-of-use assets | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	268
Right-of-use assets | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(78)
Right-of-use assets | Buildings
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	116
Additions	9
Disposals	(1)
Depreciation and impairment	(6)
Effects of changes in foreign exchange rates	0
Ending balance	118
Right-of-use assets | Buildings | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	142
Right-of-use assets | Buildings | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(24)
Right-of-use assets | Machinery and Equipment
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	71
Additions	10
Disposals	0
Depreciation and impairment	(11)
Effects of changes in foreign exchange rates	(1)
Ending balance	69
Right-of-use assets | Machinery and Equipment | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	121
Right-of-use assets | Machinery and Equipment | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	(52)
Right-of-use assets | Other
Reconciliation of changes in property, plant and equipment [abstract]
Beginning balance	3
Additions	1
Disposals	0
Depreciation and impairment	(1)
Effects of changes in foreign exchange rates	0
Ending balance	3
Right-of-use assets | Other | Cost
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	5
Right-of-use assets | Other | Less accumulated depreciation and impairment
Reconciliation of changes in property, plant and equipment [abstract]
Ending balance	€ (2)

PROPERTY, PLANT AND EQUIPMENT_3

PROPERTY, PLANT AND EQUIPMENT - Additional Information (Details) - EUR (€)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of detailed information about property, plant and equipment [abstract]
Expense related to short-term leases, low value asset leases and variable lease still recognized as operating expenses	€ 6,000,000	€ 7,000,000
Impairment charges related to cash-generating units	€ 0
Average percentage of operating level of plants	50.00%
Impairment loss recognised in profit or loss, property, plant and equipment	€ 5,000,000

INTANGIBLE ASSETS (INCLUDING _3

INTANGIBLE ASSETS (INCLUDING GOODWILL) - Changes in Intangible Assets and Goodwill (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)
Changes in goodwill [abstract]
Goodwill, beginning balance	€ 455
Effects of changes in foreign exchange rates	1
Goodwill, ending balance	456
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	70
Additions	3
Amortization expense	(5)
Transfer during the year	0
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	68
Cost
Changes in goodwill [abstract]
Goodwill, ending balance	456
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	220
Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	(152)
Technology
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	21
Additions	0
Amortization expense	(1)
Transfer during the year	0
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	20
Technology | Cost
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	86
Technology | Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	(66)
Computer Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	19
Additions	0
Amortization expense	(4)
Transfer during the year	1
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	16
Computer Software | Cost
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	75
Computer Software | Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	(59)
Customer relationships
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	14
Additions	0
Amortization expense	0
Transfer during the year	0
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	14
Customer relationships | Cost
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	40
Customer relationships | Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	(26)
Work in Progress
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	14
Additions	3
Amortization expense	0
Transfer during the year	(1)
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	16
Work in Progress | Cost
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	17
Work in Progress | Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	(1)
Other
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), beginning balance	2
Additions	0
Amortization expense	0
Transfer during the year	0
Effects of changes in foreign exchange rates	0
Intangible assets (excluding goodwill), ending balance	2
Other | Cost
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	2
Other | Less accumulated depreciation and impairment
Changes in intangible assets other than goodwill [abstract]
Intangible assets (excluding goodwill), ending balance	€ 0

TRADE PAYABLES AND OTHER (Detai

TRADE PAYABLES AND OTHER (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Non-current
Trade payables	€ 0	€ 0
Fixed assets payables	0	0
Employees' entitlements	0	0
Taxes payable other than income tax	0	0
Contract liabilities and other liabilities to customers	5	6
Other payables	14	15
Total other	19	21
Total trade payables and other	19	21
Current
Trade payables	683	711
Fixed assets payables	29	43
Employees' entitlements	173	171
Taxes payable other than income tax	33	14
Contract liabilities and other liabilities to customers	78	54
Other payables	7	6
Total other	320	288
Total trade payables and other	€ 1,003	€ 999

TRADE PAYABLES AND OTHER - Cont

TRADE PAYABLES AND OTHER - Contract Liabilities (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	€ 5	€ 6
Current	78	54
Deferred tooling revenue
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	2	2
Current	0	0
Advance payment from customers
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	1	2
Current	4	5
Unrecognized variable consideration
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	2	2
Current	57	46
Other
Disclosure of disaggregation of contract liabilities with customers [line items]
Non-current	0	0
Current	€ 17	€ 3

TRADE PAYABLES AND OTHER - Addi

TRADE PAYABLES AND OTHER - Additional Information (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)
Trade and other payables [abstract]
Revenue recognized related to contract liabilities	€ 14
Deferred revenue related to contract liabilities	€ 25

BORROWINGS - Borrowings by Natu

BORROWINGS - Borrowings by Nature (Details)	May 13, 2020EUR (€)	Jun. 30, 2020EUR (€)	Dec. 31, 2019EUR (€)	Jun. 30, 2020USD ($)	Jun. 30, 2020CHF (SFr)	May 22, 2020EUR (€)	Apr. 24, 2020EUR (€)	Aug. 08, 2019EUR (€)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 2,530,000,000
Arrangement fees		(29,000,000)
Accrued interests		35,000,000
Gross lease liabilities		190,000,000
Interest accrued lease liabilities		1,000,000
Leases		191,000,000	€ 188,000,000
Borrowings		2,536,000,000	2,361,000,000
Non-current borrowings		2,434,000,000	2,160,000,000
Current borrowings		102,000,000	201,000,000
Secured Pan-U.S. ABL (due 2022)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 0		$ 0
Effective rate		3.43%		3.43%	3.43%
Borrowings		€ 0	127,000,000
Secured U.S. DDTL (due 2022)
Disclosure of detailed information about borrowings [line items]
Nominal value | $				$ 0
Borrowings		0	0				€ 166,000,000
Secured PGE Loan (due 2025)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 180,000,000		$ 180,000,000
Effective rate		2.50%		2.50%	2.50%
Borrowings		€ 180,000,000	0
Secured PGE Loan (due 2025) | French State
Disclosure of detailed information about borrowings [line items]
Borrowings	€ 180,000,000
Percentage of principal outstanding amount guaranteed	80.00%
Option to extend period	5 years
Secured PGE Loan (due 2025) | French State | BPI France
Disclosure of detailed information about borrowings [line items]
Borrowings	€ 30,000,000
Secured Inventory Based Facility (due 2021)
Disclosure of detailed information about borrowings [line items]
Borrowings		0	0
Constellium SE (Issued May 2014, due 2024)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 357,000,000		$ 400,000,000
Nominal rate		5.75%
Effective rate		6.26%		6.26%	6.26%
Arrangement fees		€ (3,000,000)
Accrued interests		3,000,000
Borrowings		357,000,000	€ 355,000,000
Constellium SE (Issued May 2014, due 2021)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 0
Nominal rate		4.63%	4.625%
Effective rate		5.16%		5.16%	5.16%
Arrangement fees		€ 0
Accrued interests		0
Borrowings		0	€ 200,000,000					€ 300,000,000
Constellium SE (Issued February 2017, due 2025)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 580,000,000		$ 650,000,000
Nominal rate		6.63%
Effective rate		7.13%		7.13%	7.13%
Arrangement fees		€ (9,000,000)
Accrued interests		13,000,000
Borrowings		584,000,000	582,000,000
Constellium SE (Issued November 2017, due 2026)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 447,000,000		$ 500,000,000
Nominal rate		5.88%
Effective rate		6.26%		6.26%	6.26%
Arrangement fees		€ (6,000,000)
Accrued interests		10,000,000
Borrowings		451,000,000	449,000,000
Constellium SE (Issued November 2017, due 2026)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 400,000,000
Nominal rate		4.25%
Effective rate		4.57%		4.57%	4.57%
Arrangement fees		€ (5,000,000)
Accrued interests		6,000,000
Borrowings		401,000,000	400,000,000
Constellium SE (Issued June 2020, due 2028)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 290,000,000		$ 325,000,000
Nominal rate		5.625%
Effective rate		6.05%		6.05%	6.05%
Arrangement fees		€ (6,000,000)
Accrued interests		0
Borrowings		284,000,000	0
Unsecured Revolving Credit Facility (due 2021)
Disclosure of detailed information about borrowings [line items]
Borrowings		0	0
Unsecured Revolving Credit Facility (due 2021) | BPI France
Disclosure of detailed information about borrowings [line items]
Borrowing capacity		5,000,000
Unsecured Credit facility Switzerland (due 2025)
Disclosure of detailed information about borrowings [line items]
Nominal value		€ 18,000,000			SFr 19,500,000
Nominal rate		1.18%
Effective rate		1.18%		1.18%	1.18%
Borrowings		€ 18,000,000	0
Unsecured Credit facility Switzerland (due 2025) | Swiss State
Disclosure of detailed information about borrowings [line items]
Borrowings						€ 20,000,000
Percentage of principal outstanding amount guaranteed						85.00%
Other loans
Disclosure of detailed information about borrowings [line items]
Nominal value		68,000,000
Accrued interests		2,000,000
Borrowings		70,000,000	€ 60,000,000
Financing Arrangements
Disclosure of detailed information about borrowings [line items]
Borrowings		€ 38,000,000

BORROWINGS - Movement in Borrow

BORROWINGS - Movement in Borrowings (Details) € in Millions	Aug. 08, 2019EUR (€)	Jun. 30, 2020EUR (€)	Jun. 30, 2019EUR (€)	Dec. 31, 2019EUR (€)
Disclosure of detailed information about borrowings [line items]
Beginning Balance		€ 2,361
Proceeds from issuance of Senior Notes		290	€ 0	€ 0
(Repayments) of Senior Notes		(200)	0	(100)
Proceeds from non-current borrowings		180		0
Proceeds from Swiss credit facility		18	0	0
(Repayments) / proceeds from U.S. revolving credit facility and other loans		(124)		109
Arrangement fees payment		(6)		0
Lease repayments		(17)		(86)
Borrowings assumed through business combination		0		75
Movement in interests accrued or capitalized		(1)		1
New leases and other loans		25		75
Deferred arrangement fees and other		3		5
Effects of changes in foreign exchange rates		7		29
Ending Balance		€ 2,536		2,361
Exchange rate		1.1198
Constellium SE (Issued May 2014, due 2021)
Disclosure of detailed information about borrowings [line items]
Beginning Balance		€ 200
(Repayments) of Senior Notes	€ (100)
Ending Balance	€ 300	€ 0		€ 200
Nominal rate		4.63%		4.625%
Previously stated
Disclosure of detailed information about borrowings [line items]
Beginning Balance			2,151	€ 2,151
IFRS 16 application | IFRS 16
Disclosure of detailed information about borrowings [line items]
Beginning Balance			102	102
Restated | IFRS 16
Disclosure of detailed information about borrowings [line items]
Beginning Balance			€ 2,253	€ 2,253

BORROWINGS - Currency Concentra

BORROWINGS - Currency Concentration of Total Borrowings (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of detailed information about borrowings [line items]
Borrowings	€ 2,536	€ 2,361
U.S. Dollars
Disclosure of detailed information about borrowings [line items]
Borrowings	1,757	1,597
Euro
Disclosure of detailed information about borrowings [line items]
Borrowings	741	746
Other currencies
Disclosure of detailed information about borrowings [line items]
Borrowings	€ 38	€ 18

BORROWINGS - Additional Informa

BORROWINGS - Additional Information (Details)	6 Months Ended
	Jun. 30, 2020
Secured Pan-U.S. ABL (due 2022)
Disclosure of detailed information about borrowings [line items]
Debt covenant, percentage of aggregate revolving loan commitments	10.00%

FINANCIAL INSTRUMENTS - Financi

FINANCIAL INSTRUMENTS - Financial Assets and Liabilities by Categories (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of detailed information about financial instruments [line items]
Financial assets	€ 795	€ 606
Financial liabilities	3,323	3,173
Trade payables and fixed assets payables
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	712	754
Borrowings
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	2,536	2,361
Other financial liabilities
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	75	58
At amortized cost
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	3,248	3,115
At amortized cost | Trade payables and fixed assets payables
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	712	754
At amortized cost | Borrowings
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	2,536	2,361
At amortized cost | Other financial liabilities
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0	0
At Fair Value through Profit and loss
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	61	44
At Fair Value through Profit and loss | Trade payables and fixed assets payables
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0	0
At Fair Value through Profit and loss | Borrowings
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0	0
At Fair Value through Profit and loss | Other financial liabilities
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	61	44
At Fair Value through OCI
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	14	14
At Fair Value through OCI | Trade payables and fixed assets payables
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0	0
At Fair Value through OCI | Borrowings
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0	0
At Fair Value through OCI | Other financial liabilities
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	14	14
Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Financial assets	378	184
Trade receivables
Disclosure of detailed information about financial instruments [line items]
Financial assets	386	393
Other financial assets
Disclosure of detailed information about financial instruments [line items]
Financial assets	31	29
At amortized cost
Disclosure of detailed information about financial instruments [line items]
Financial assets	378	184
At amortized cost | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Financial assets	378	184
At amortized cost | Trade receivables
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
At amortized cost | Other financial assets
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
At Fair Value through Profit and loss
Disclosure of detailed information about financial instruments [line items]
Financial assets	31	29
At Fair Value through Profit and loss | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
At Fair Value through Profit and loss | Trade receivables
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
At Fair Value through Profit and loss | Other financial assets
Disclosure of detailed information about financial instruments [line items]
Financial assets	31	29
At Fair Value through OCI
Disclosure of detailed information about financial instruments [line items]
Financial assets	386	393
At Fair Value through OCI | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
At Fair Value through OCI | Trade receivables
Disclosure of detailed information about financial instruments [line items]
Financial assets	386	393
At Fair Value through OCI | Other financial assets
Disclosure of detailed information about financial instruments [line items]
Financial assets	€ 0	€ 0

FINANCIAL INSTRUMENTS - Other F

FINANCIAL INSTRUMENTS - Other Financial Assets and Other Financial Liabilities Positions (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	€ 9	€ 7
Current derivatives assets	22	22
Derivatives assets	31	29
Other non-current financial assets	9	7
Other current financial assets	22	22
Other financial assets	31	29
Non-current derivatives liabilities	30	23
Current derivative liabilities	45	35
Derivatives liabilities	75	58
Other non-current financial liabilities	30	23
Other current financial liabilities	45	35
Other financial liabilities	75	58
Aluminium and premium future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives liabilities	9	4
Current derivative liabilities	19	10
Derivatives liabilities	28	14
Energy future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives liabilities	0	0
Current derivative liabilities	0	1
Derivatives liabilities	0	1
Other future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives liabilities	1	2
Current derivative liabilities	4	4
Derivatives liabilities	5	6
Currency commercial contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives liabilities	15	12
Current derivative liabilities	21	16
Derivatives liabilities	36	28
Currency net debt derivatives
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives liabilities	5	5
Current derivative liabilities	1	4
Derivatives liabilities	6	9
Aluminium and premium future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	2	1
Current derivatives assets	11	8
Derivatives assets	13	9
Energy future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	0	0
Current derivatives assets	0	0
Derivatives assets	0	0
Other future contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	0	0
Current derivatives assets	0	0
Derivatives assets	0	0
Currency commercial contracts
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	7	5
Current derivatives assets	10	12
Derivatives assets	17	17
Currency net debt derivatives
Disclosure of detailed information about financial instruments [line items]
Non-current derivatives assets	0	1
Current derivatives assets	1	2
Derivatives assets	€ 1	€ 3

FINANCIAL INSTRUMENTS - Additio

FINANCIAL INSTRUMENTS - Additional Information (Details) - Fair value - Level 1 € in Millions	Jun. 30, 2020EUR (€)
Constellium SE (Issued May 2014, due 2024)
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	100.50%
Senior notes issued	€ 359
Constellium N.V. Senior Unsecured Notes (Issued February 2017, due 2025)
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	101.60%
Senior notes issued	€ 589
Constellium N.V. EUR and USD Senior Unsecured Notes (Issued November 2017, due 2026)
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	99.70%
Senior notes issued	€ 844
Constellium SE (Issued June 2020, due 2028)
Disclosure of detailed information about financial instruments [line items]
Percentage of fair value senior notes issued	99.80%
Senior notes issued	€ 289

FINANCIAL INSTRUMENTS - Derivat

FINANCIAL INSTRUMENTS - Derivatives Measured at Fair Value (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of financial instruments measured at fair value [line items]
Other financial assets - derivatives	€ 31	€ 29
Other financial liabilities - derivatives	75	58
Level 1
Disclosure of financial instruments measured at fair value [line items]
Other financial assets - derivatives	12	8
Other financial liabilities - derivatives	30	19
Level 2
Disclosure of financial instruments measured at fair value [line items]
Other financial assets - derivatives	19	21
Other financial liabilities - derivatives	45	39
Level 3
Disclosure of financial instruments measured at fair value [line items]
Other financial assets - derivatives	0	0
Other financial liabilities - derivatives	€ 0	€ 0

FINANCIAL RISK MANAGEMENT - Add

FINANCIAL RISK MANAGEMENT - Additional Information (Details) € in Millions, SFr in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019EUR (€)	Jun. 30, 2020EUR (€)	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 30, 2019EUR (€)	Jun. 30, 2019CHF (SFr)	Dec. 31, 2018EUR (€)
Disclosure of liquidity risk [line items]
Revolving credit facilities outstanding	€ 281	€ 506
Liquidity value	516	949
Cash and cash equivalents	184	378			€ 213		€ 164
Undrawn facilities	332	571
Secured Pan-U.S. ABL (due 2022)
Disclosure of liquidity risk [line items]
Borrowing base | $			$ 322	$ 375
Secured U.S. DDTL (due 2022)
Disclosure of liquidity risk [line items]
Borrowing base | $			166
French inventory facility
Disclosure of liquidity risk [line items]
Borrowing base	82	€ 78
Forward contract
Disclosure of liquidity risk [line items]
Total nominal amount forward contracts | SFr						SFr 174
Unrealized loss of the net investment hedge	€ 3
Derivative classified as cash flow hedge
Disclosure of liquidity risk [line items]
Nominal amount hedging instrument | $			109	$ 233
Derivative classified as cash flow hedge | Foreign exchange forward contracts
Disclosure of liquidity risk [line items]
Nominal amount hedging instrument | $			$ 255

FINANCIAL RISK MANAGEMENT - Eff

FINANCIAL RISK MANAGEMENT - Effect of Foreign Currency Derivatives Impacts and Commercial Transactions Exposures (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized gains / (losses) on foreign currency derivatives - net	€ (3)	€ 0	€ (3)	€ 1
Unrealized gains / (losses) on foreign currency derivatives - net	0	(1)	(2)	1
Losses reclassified from OCI as a result of hedge accounting discontinuation	(5)	0	(5)	0
Included in Other gains / (losses) - net
Disclosure of nature and extent of risks arising from financial instruments [line items]
Losses reclassified from OCI as a result of hedge accounting discontinuation	(5)	0	(5)	0
Derivatives that do not qualify for hedge accounting | Included in Other gains / (losses) - net
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized gains / (losses) on foreign currency derivatives - net	0	1	2	3
Unrealized gains / (losses) on foreign currency derivatives - net	(1)	(1)	(2)	1
Derivatives that qualify for hedge accounting | Included in Revenue
Disclosure of nature and extent of risks arising from financial instruments [line items]
Realized gains / (losses) on foreign currency derivatives - net	(3)	(1)	(5)	(2)
Unrealized gains / (losses) on foreign currency derivatives - net	1	0	0	0
Derivatives that qualify for hedge accounting | Included in Other comprehensive income / (loss)
Disclosure of nature and extent of risks arising from financial instruments [line items]
Unrealized gains / (losses) on foreign currency derivatives - net	2	1	(6)	(7)
Gains reclassified from cash flow hedge reserve to the Unaudited Interim Consolidated Income Statement	€ 3	€ 1	€ 6	€ 2

PENSIONS AND OTHER POST-EMPLO_3

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Actuarial Assumptions (Details)	Jun. 30, 2020	Dec. 31, 2019
Switzerland
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.20%	0.15%
U.S. | Hourly pension | Bottom of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.70%	3.15%
U.S. | Hourly pension | Top of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.85%	3.25%
U.S. | Salaried pension
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.75%	3.25%
U.S. | OPEB | Bottom of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.70%	3.20%
U.S. | OPEB | Top of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.00%	3.40%
U.S. | Other benefits | Bottom of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.45%	3.00%
U.S. | Other benefits | Top of range
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	2.75%	3.20%
France | Retirements
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.95%	0.95%
France | Other benefits
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	0.85%	0.80%
Germany
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	1.05%	1.00%

PENSIONS AND OTHER POST-EMPLO_4

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Amounts Recognized in the Consolidated Statement of Financial Position (Details) - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of net defined benefit liability (asset) [line items]
Present value of funded obligation	€ 789	€ 768
Fair value of plan assets	(435)	(445)
Deficit of funded plans	354	323
Present value of unfunded obligation	361	347
Net liability arising from defined benefit obligation	715	670
Pension Benefits
Disclosure of net defined benefit liability (asset) [line items]
Present value of funded obligation	789	768
Fair value of plan assets	(435)	(445)
Deficit of funded plans	354	323
Present value of unfunded obligation	131	127
Net liability arising from defined benefit obligation	485	450
Other Benefits
Disclosure of net defined benefit liability (asset) [line items]
Present value of funded obligation	0	0
Fair value of plan assets	0	0
Deficit of funded plans	0	0
Present value of unfunded obligation	230	220
Net liability arising from defined benefit obligation	€ 230	€ 220

PENSIONS AND OTHER POST-EMPLO_5

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Amounts Recognized in the Consolidated Income Statement (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Included in the Unaudited Interim Consolidated Income Statement
Disclosure of defined benefit plans [line items]
Current service cost	€ (6)	€ (6)	€ (14)	€ (12)
Past service cost	(2)	0	(2)	0
Net interest	(3)	(4)	(6)	(8)
Immediate recognition of gains / (losses) arising over the period	(1)	(2)	0	(2)
Administration expenses	(1)	0	(1)	(1)
Total	(13)	(12)	(23)	(23)
Pension Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of defined benefit plans [line items]
Current service cost	(5)	(5)	(11)	(9)
Past service cost	0	0	0	0
Net interest	(2)	(2)	(3)	(4)
Immediate recognition of gains / (losses) arising over the period	0	0	0	0
Administration expenses	(1)	0	(1)	(1)
Total	(8)	(7)	(15)	(14)
Other Benefits
Disclosure of defined benefit plans [line items]
Past service cost			(2)		€ (3)	€ (36)
Other Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of defined benefit plans [line items]
Current service cost	(1)	(1)	(3)	(3)
Past service cost	(2)	0	(2)	0
Net interest	(1)	(2)	(3)	(4)
Immediate recognition of gains / (losses) arising over the period	(1)	(2)	0	(2)
Administration expenses	0	0	0	0
Total	€ (5)	€ (5)	€ (8)	€ (9)

PENSIONS AND OTHER POST-EMPLO_6

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Movement in Net Defined Benefit Obligations (Details) € in Millions, $ in Millions	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2020EUR (€)	Jun. 30, 2019EUR (€)	Jun. 30, 2020EUR (€)	Jun. 30, 2020USD ($)	Jun. 30, 2019EUR (€)	Dec. 31, 2019EUR (€)	Dec. 31, 2018EUR (€)
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			€ 670	$ 670
Remeasurements due to:
Closing balance	€ 715		715			€ 670
Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	6	€ 6	14		€ 12
Interest cost / (income)	3	4	6		8
Past service cost	2	0	2		0
Immediate recognition of gains / (losses) arising over the year	1	2	0		2
Administration expenses	1	0	1		1
Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			13
—changes in financial assumptions			27
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			2
Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(10)
Contributions by the Group			(10)
Contributions by the plan participants			0
Pension Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	5	5	11		9
Interest cost / (income)	2	2	3		4
Past service cost	0	0	0		0
Immediate recognition of gains / (losses) arising over the year	0	0	0		0
Administration expenses	1	0	1		1
Other Benefits
Disclosure of net defined benefit liability (asset) [line items]
Past service cost			2			3	€ 36
Other Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	1	1	3		3
Interest cost / (income)	1	2	3		4
Past service cost	2	0	2		0
Immediate recognition of gains / (losses) arising over the year	1	2	0		2
Administration expenses	0	€ 0	0		€ 0
Defined benefit obligations
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			1,115
Remeasurements due to:
Closing balance	1,150		1,150			1,115
Defined benefit obligations | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			14
Interest cost / (income)			10
Past service cost			2
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			27
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			7
Defined benefit obligations | Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(27)
Contributions by the Group			0
Contributions by the plan participants			2
Defined benefit obligations | Pension Benefits
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			895
Remeasurements due to:
Closing balance	920		920			895
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			11
Interest cost / (income)			7
Past service cost			0
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			16
—changes in demographic assumptions			0
—experience losses			1
Effects of changes in foreign exchange rates			6
Defined benefit obligations | Pension Benefits | Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(18)
Contributions by the Group			0
Contributions by the plan participants			2
Defined benefit obligations | Other Benefits
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			220
Remeasurements due to:
Closing balance	230		230			220
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			3
Interest cost / (income)			3
Past service cost			2
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			0
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			0
—changes in financial assumptions			11
—changes in demographic assumptions			0
—experience losses			(1)
Effects of changes in foreign exchange rates			1
Defined benefit obligations | Other Benefits | Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			(9)
Contributions by the Group			0
Contributions by the plan participants			0
Plan Assets
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance			(445)
Remeasurements due to:
Closing balance	€ (435)		(435)			€ (445)
Plan Assets | Included in the Unaudited Interim Consolidated Income Statement
Disclosure of net defined benefit liability (asset) [line items]
Current service cost			0
Interest cost / (income)			(4)
Past service cost			0
Immediate recognition of gains / (losses) arising over the year			0
Administration expenses			1
Plan Assets | Included in the Unaudited Interim Consolidated Statement of Comprehensive Income / (Loss)
Remeasurements due to:
—actual return less interest on plan assets			13
—changes in financial assumptions			0
—changes in demographic assumptions			0
—experience losses			0
Effects of changes in foreign exchange rates			(5)
Plan Assets | Included in the Unaudited Interim Consolidated Statement of Cash Flows
Remeasurements due to:
Benefits paid			17
Contributions by the Group			(10)
Contributions by the plan participants			€ (2)

PENSIONS AND OTHER POST-EMPLO_7

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Additional Information (Details) - EUR (€) € in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Benefits
Disclosure of defined benefit plans [line items]
Gain recognized on negative past service costs	€ 2	€ 3	€ 36

PENSIONS AND OTHER POST-EMPLO_8

PENSIONS AND OTHER POST-EMPLOYMENT BENEFIT OBLIGATIONS - Net Defined Benefit Obligations by Country (Details) € in Millions, $ in Millions	Jun. 30, 2020EUR (€)	Dec. 31, 2019EUR (€)	Dec. 31, 2019USD ($)
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	€ 1,150	€ 1,115
Plan assets	(435)	(445)
Net defined benefit liability	715	670	$ 670
France
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	164	161
Plan assets	(3)	(3)
Net defined benefit liability	161	158
Germany
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	140	144
Plan assets	(1)	(1)
Net defined benefit liability	139	143
Switzerland
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	303	299
Plan assets	(213)	(214)
Net defined benefit liability	90	85
United States
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	542	510
Plan assets	(218)	(227)
Net defined benefit liability	324	283
Other
Disclosure of net defined benefit liability (asset) [line items]
Defined benefit obligations	1	1
Plan assets	0	0
Net defined benefit liability	€ 1	€ 1

PROVISIONS - Changes in Provisi

PROVISIONS - Changes in Provisions (Details) - EUR (€) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Changes in other provisions [abstract]
Beginning balance			€ 122
Allowance			13
Amounts used			(5)
Unused amounts reversed			(4)
Unwinding of discounts			1
Effects of changes in foreign exchange rates			1
Ending balance	€ 128		128
Current					€ 29	€ 23
Non-Current					99	99
Total Provisions	128		128		128	122
Adjustments for restructuring costs	11	€ 1	11	€ 1
Close down and environmental remediation costs
Changes in other provisions [abstract]
Beginning balance			90
Allowance			0
Amounts used			0
Unused amounts reversed			0
Unwinding of discounts			1
Effects of changes in foreign exchange rates			1
Ending balance	92		92
Current					7
Non-Current					85
Total Provisions	92		92		92	90
Restructuring costs
Changes in other provisions [abstract]
Beginning balance			4
Allowance			11
Amounts used			(5)
Unused amounts reversed			0
Unwinding of discounts			0
Effects of changes in foreign exchange rates			0
Ending balance	10		10
Current					9
Non-Current					1
Total Provisions	10		10		10	4
Legal claims and other costs
Changes in other provisions [abstract]
Beginning balance			28
Allowance			2
Amounts used			0
Unused amounts reversed			(4)
Unwinding of discounts			0
Effects of changes in foreign exchange rates			0
Ending balance	26		26
Current					13
Non-Current					13
Total Provisions	€ 26		€ 26		€ 26	€ 28

PROVISIONS - Legal Claims and O

PROVISIONS - Legal Claims and Other Costs (Details) - Legal claims and other costs - EUR (€) € in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of other provisions [line items]
Litigation	€ 19	€ 21
Disease claims	4	4
Other	3	3
Total Provisions for legal claims and other costs	€ 26	€ 28

NON-CASH INVESTING AND FINANC_2

NON-CASH INVESTING AND FINANCING TRANSACTIONS (Details) - EUR (€) € in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Disclosure of cash flow statement [Abstract]
Property, plant and equipment acquired by finance lease	€ 25	€ 33
Fair value of vested PSUs and RSUs	€ 0	€ 4

SHARE CAPITAL - Additional Info

SHARE CAPITAL - Additional Information (Details)	Jun. 30, 2020EUR (€)€ / sharesshares	Dec. 31, 2019EUR (€)shares
Disclosure of classes of share capital [line items]
Share capital | €	€ 2,758,440.64	€ 3,000,000
Nominal value of ordinary fully-paid shares (in EUR per share) | € / shares	€ 0.02
Number of vote rights per share	1
Ordinary shares
Disclosure of classes of share capital [line items]
Number of ordinary shares (in shares) | shares	137,922,032	137,867,418

SHARE CAPITAL (Details)

SHARE CAPITAL (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)shares
Disclosure of classes of share capital [line items]
Beginning balance	€ (85)
Ending balance	(174)
Share capital
Disclosure of classes of share capital [line items]
Beginning balance	3
New shares issued	0
Ending balance	3
Share premium
Disclosure of classes of share capital [line items]
Beginning balance	420
New shares issued	0
Ending balance	€ 420
Ordinary shares
Disclosure of classes of share capital [line items]
Beginning balance (in shares) | shares	137,867,418
New shares issued (in shares) | shares	54,614
Ending balance (in shares) | shares	137,922,032

SHARE-BASED COMPENSATION - Addi

SHARE-BASED COMPENSATION - Additional Information (Details) - EUR (€) € in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Share Based Payment Plans [line items]
Total expense related to the potential ordinary shares	€ 8	€ 7
PSUs
Share Based Payment Plans [line items]
Share based compensation vesting period	3 years
PSUs | Bottom of range
Share Based Payment Plans [line items]
Percentage of vesting multiplier	0.00%
PSUs | Top of range
Share Based Payment Plans [line items]
Percentage of vesting multiplier	200.00%
RSUs
Share Based Payment Plans [line items]
Share based compensation vesting period	3 years

SHARE-BASED COMPENSATION - Inpu

SHARE-BASED COMPENSATION - Inputs to the Model Used for PSUs Granted (Details) - PSUs	6 Months Ended
	Jun. 30, 2020€ / shares
Disclosure of Input of Model Used for Performance-Based RSU [Line Items]
Fair value at grant date (in euros)	€ 6.65
Share price at grant date (in euros)	€ 4.64
Dividend yield	0.00%
Expected volatility	63.00%
Risk-free interest rate (US government bond yield)	0.36%

SHARE-BASED COMPENSATION - Numb

SHARE-BASED COMPENSATION - Number and Movement of Potential Shares (Details)	6 Months Ended
	Jun. 30, 2020shares
Performance Share Units (PSUs)
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance (in shares)	2,519,294
Potential Shares, Granted (in shares)	1,049,839
Potential Shares, Vested (in shares)	0
Potential Shares, Forfeited (in shares)	(46,306)
Potential Shares, Ending balance (in shares)	3,522,827
Percentage of vesting multiplier	100.00%
Performance based shares forfeited upon departure of certain beneficiaries (in shares)	46,306
Performance based shares forfeited upon non-fulfillment of performance conditions (in shares)	0
Restricted Stock Units (RSUs)
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance (in shares)	2,066,503
Potential Shares, Granted (in shares)	910,047
Potential Shares, Vested (in shares)	(8,000)
Potential Shares, Forfeited (in shares)	(50,931)
Potential Shares, Ending balance (in shares)	2,917,619
Equity Award Plans
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance (in shares)	79,526
Potential Shares, Granted (in shares)	0
Potential Shares, Vested (in shares)	(46,614)
Potential Shares, Forfeited (in shares)	0
Potential Shares, Ending balance (in shares)	32,912
Total Potential Shares
Disclosure of movement of potential shares [line items]
Potential Shares, Beginning balance (in shares)	4,665,323
Potential Shares, Granted (in shares)	1,959,886
Potential Shares, Vested (in shares)	(54,614)
Potential Shares, Forfeited (in shares)	(97,237)
Potential Shares, Ending balance (in shares)	6,473,358

COVID-19-RELATED GOVERNMENT A_2

COVID-19-RELATED GOVERNMENT ASSISTANCE (Details) € in Millions	6 Months Ended
	Jun. 30, 2020EUR (€)
Government Assistance [Abstract]
Proceeds From Government Assistance	€ 14

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) € in Millions	Jul. 15, 2020EUR (€)credit_facility	Jun. 30, 2020EUR (€)	Dec. 31, 2019EUR (€)
Disclosure of non-adjusting events after reporting period [line items]
Borrowings		€ 2,536	€ 2,361
Entering Into New Credit Facilities | Constellium Singen GmbH and Constellium Singen Rolled Products | Guaranteed Credit Facilities | German State
Disclosure of non-adjusting events after reporting period [line items]
Number of credit facilities | credit_facility	2
Borrowings	€ 50
Percentage of principal outstanding amount guaranteed	80.00%