Alcoa (AA) 10-Q 9 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 03, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	AA
Entity Registrant Name	ALCOA CORP
Entity Central Index Key	1,675,149
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		186,455,843

Statement of Consolidated Opera

Statement of Consolidated Operations (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Sales (C & E)	$ 3,090	$ 2,655
Cost of goods sold (exclusive of expenses below)	2,381	2,023
Selling, general administrative, and other expenses	67	71
Research and development expenses	8	7
Provision for depreciation, depletion, and amortization	194	179
Restructuring and other charges (D)	(19)	10
Interest expense	26	26
Other expenses (income), net (N)	21	(79)
Total costs and expenses	2,678	2,237
Income before income taxes	412	418
Provision for income taxes	138	110
Net income	274	308
Less: Net income attributable to noncontrolling interest	124	83
Consolidated net income attributable to Alcoa Corporation	$ 150	$ 225
EARNINGS PER SHARE ATTRIBUTABLE TO ALCOA CORPORATION COMMON SHAREHOLDERS (F):
Basic	$ 0.81	$ 1.23
Diluted	$ 0.80	$ 1.21

Statement of Consolidated Compr

Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 274	$ 308
Other comprehensive income (loss), net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	102	43
Foreign currency translation adjustments	(13)	353
Net change in unrecognized gains/losses on cash flow hedges	530	(225)
Total Other comprehensive income (loss), net of tax	619	171
Comprehensive income	893	479
Alcoa Corporation [Member]
Net income	150	225
Other comprehensive income (loss), net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	101	44
Foreign currency translation adjustments	1	239
Net change in unrecognized gains/losses on cash flow hedges	550	(308)
Total Other comprehensive income (loss), net of tax	652	(25)
Comprehensive income	802	200
Non-controlling Interest [Member]
Net income	124	83
Other comprehensive income (loss), net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	1	(1)
Foreign currency translation adjustments	(14)	114
Net change in unrecognized gains/losses on cash flow hedges	(20)	83
Total Other comprehensive income (loss), net of tax	(33)	196
Comprehensive income	$ 91	$ 279

Consolidated Balance Sheet (una

Consolidated Balance Sheet (unaudited) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents (K)	$ 1,196	$ 1,358
Receivables from customers	814	811
Other receivables	187	232
Inventories (I)	1,630	1,453
Fair value of derivative contracts (O)	52	113
Prepaid expenses and other current assets	270	271
Total current assets	4,149	4,238
Properties, plants, and equipment	22,837	23,046
Less: accumulated depreciation, depletion, and amortization	13,803	13,908
Properties, plants, and equipment, net	9,034	9,138
Investments (H & M)	1,413	1,410
Deferred income taxes	700	814
Fair value of derivative contracts (K)	99	128
Other noncurrent assets	1,701	1,719
Total assets	17,096	17,447
Current liabilities:
Accounts payable, trade	1,813	1,898
Accrued compensation and retirement costs	416	459
Taxes, including income taxes	325	282
Fair value of derivative contracts (O)	113	185
Other current liabilities	294	412
Long-term debt due within one year (K)	15	16
Total current liabilities	2,976	3,252
Long-term debt, less amount due within one year (K)	1,445	1,388
Accrued pension benefits	2,218	2,341
Accrued other postretirement benefits	1,075	1,100
Asset retirement obligations	631	617
Environmental remediation (M)	234	258
Fair value of derivative contracts (K)	466	1,105
Noncurrent income taxes	285	309
Other noncurrent liabilities and deferred credits	249	279
Total liabilities	9,579	10,649
CONTINGENCIES AND COMMITMENTS (M)
Alcoa Corporation shareholders' equity:
Common stock	2	2
Additional capital	9,633	9,590
Retained earnings	263	113
Accumulated other comprehensive loss (G)	(4,530)	(5,182)
Total Alcoa Corporation shareholders' equity	5,368	4,523
Noncontrolling interest	2,149	2,275
Total equity	7,517	6,798
Total liabilities and equity	$ 17,096	$ 17,447

Statement of Consolidated Cash

Statement of Consolidated Cash Flows (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FROM OPERATIONS
Net income	$ 274	$ 308
Adjustments to reconcile net income to cash from operations:
Depreciation, depletion, and amortization	194	179
Deferred income taxes	(11)	23
Equity earnings, net of dividends	(6)	(1)
Restructuring and other charges (D)	(19)	10
Net gain from investing activities - asset sales (N)	(5)	(120)
Net periodic pension benefit cost (J)	40	28
Stock-based compensation	10	7
Other	(14)	9
Changes in assets and liabilities, excluding effects of acquisitions, divestitures, and foreign currency translation adjustments:
Decrease in receivables	43	7
(Increase) in inventories	(169)	(102)
Decrease in prepaid expenses and other current assets	2	13
(Decrease) in accounts payable, trade	(106)	(45)
(Decrease) in accrued expenses	(186)	(181)
Increase (Decrease) in taxes, including income taxes	84	(17)
Pension contributions	(40)	(21)
(Increase) in noncurrent assets	(13)	(3)
(Decrease) in noncurrent liabilities	(23)	(20)
CASH PROVIDED FROM OPERATIONS	55	74
FINANCING ACTIVITIES
Cash paid to former parent company related to separation		(238)
Net change in short-term borrowings (original maturities of three months or less)		2
Additions to debt (original maturities greater than three months)	61	2
Payments on debt (original maturities greater than three months)	(4)	(5)
Proceeds from the exercise of employee stock options	15	18
Contributions from noncontrolling interest	53	24
Distributions to noncontrolling interest	(267)	(57)
Other	(5)	(6)
CASH USED FOR FINANCING ACTIVITIES	(147)	(260)
INVESTING ACTIVITIES
Capital expenditures	(74)	(71)
Proceeds from the sale of assets and businesses		238
Additions to investments		(25)
CASH (USED FOR) PROVIDED FROM INVESTING ACTIVITIES	(74)	142
EFFECT OF EXCHANGE RATE CHANGES ON CASH AND CASH EQUIVALENTS AND RESTRICTED CASH	4	7
Net change in cash and cash equivalents and restricted cash	(162)	(37)
Cash and cash equivalents and restricted cash at beginning of year (B)	1,365	859
CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AT END OF PERIOD (B)	$ 1,203	$ 822

Statement of Changes in Consoli

Statement of Changes in Consolidated Equity (unaudited) - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Capital [Member]	Retained (Deficit) Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Non-controlling Interest [Member]
Beginning Balance at Dec. 31, 2016	$ 7,697	$ 2	$ 9,531	$ (104)	$ (3,775)	$ 2,043
Net income	308			225		83
Other comprehensive (loss) income (G)	171				(25)	196
Stock-based compensation	7		7
Common stock issued: compensation plans	15		15
Contributions	24					24
Distributions	(57)					(57)
Other	(2)					(2)
Ending Balance at Mar. 31, 2017	8,163	2	9,553	121	(3,800)	2,287
Beginning Balance at Dec. 31, 2017	6,798	2	9,590	113	(5,182)	2,275
Net income	274			150		124
Other comprehensive (loss) income (G)	619				652	(33)
Stock-based compensation	10		10
Common stock issued: compensation plans	15		15
Contributions	53					53
Distributions	(267)					(267)
Other	15		18			(3)
Ending Balance at Mar. 31, 2018	$ 7,517	$ 2	$ 9,633	$ 263	$ (4,530)	$ 2,149

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	A. Basis of Presentation year-end 10-Q 10-K References in these Notes to “ParentCo” refer to Alcoa Inc., a Pennsylvania corporation, and its consolidated subsidiaries (through October 31, 2016, at which time was renamed Arconic Inc. (Arconic)). On November 1, 2016 (the “Separation Date”), ParentCo separated into two standalone, publicly-traded companies, Alcoa Corporation and Arconic (the “Separation Transaction”). In connection with the Separation Transaction, as of October 31, 2016, the Company and Arconic entered into several agreements to effect the Separation Transaction, including a Separation and Distribution Agreement and a Tax Matters Agreement. See Note A to the Consolidated Financial Statements in Part II Item 8 of Alcoa Corporation’s Annual Report on Form 10-K Principles of Consolidation. AWAC is an unincorporated global joint venture between Alcoa Corporation and Alumina Limited and consists of several affiliated operating entities, which own, or have an interest in, or operate the bauxite mines and alumina refineries within Alcoa Corporation’s Bauxite and Alumina segments (except for the Poços de Caldas mine and refinery and a portion of the São Luís refinery, all in Brazil) and the Portland smelter in Australia. Alcoa Corporation owns 60% and Alumina Limited owns 40% of these individual entities, which are consolidated by the Company for financial reporting purposes and include Alcoa of Australia Limited, Alcoa World Alumina LLC (AWA), and Alcoa World Alumina Brasil Ltda. (AWAB). Alumina Limited’s interest in the equity of such entities is reflected as Noncontrolling interest on the accompanying Consolidated Balance Sheet.

Recently Adopted and Recently I

Recently Adopted and Recently Issued Accounting Guidance	3 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	B. Recently Adopted and Recently Issued Accounting Guidance Adopted On January 1, 2018, Alcoa Corporation adopted guidance issued by the Financial Accounting Standards Board (FASB) to the recognition of revenue from contracts with customers. This guidance created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue, and, therefore, supersedes virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. Management’s assessment of this guidance was applied only to those customer contracts that were open on the date of adoption under the modified retrospective method. Through a previously established project team, the Company completed a detailed review of the terms and provisions of its customer contracts, as well as evaluated these contracts under the new guidance, throughout 2017 and concluded that Alcoa Corporation’s revenue recognition practices were in compliance with this framework. That said, the Company did make some minor modifications to its internal accounting policies and internal control structure to ensure that any future customer contracts that may have different terms and conditions of those that the Company has today are properly evaluated under the new guidance. Other than providing additional disclosure (see Note C), the adoption of this guidance had no impact on the Consolidated Financial Statements. On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to the accounting and reporting of certain equity investments. This guidance requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Additionally, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. The adoption of this guidance had no impact on the Consolidated Financial Statements, as all of Alcoa Corporation’s equity investments are accounted for under the equity method of accounting. On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to the presentation of several items in the statement of cash flows. Specifically, the guidance identifies nine cash flow items and the sections where they must be presented within the statement of cash flows, including distributions received from equity method investees, proceeds from the settlement of insurance claims, and restricted cash. Other than as it relates to restricted cash, the adoption of this guidance had no impact on the Consolidated Financial Statements. This guidance requires that restricted cash be aggregated with cash and cash equivalents in both the beginning-of-period end-of-period beginning-of-period end-of non-cash March 31, 2018 December 31, 2017 Cash and cash equivalents $ 1,196 $ 1,358 Restricted cash* 7 7 $ 1,203 $ 1,365 * These amounts are reported in Prepaid expenses and other current assets on the accompanying Consolidated Balance Sheet. On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to the accounting for intra-entity transactions, other than inventory. The guidance requires the current and deferred income tax consequences of an intra-entity transfer to be recorded immediately when the transaction occurs; the exception to defer the tax consequences of inventory transactions is maintained. Prior to this guidance, no immediate tax impact was permitted to be recognized in an entity’s financial statements as a result of intra-entity transfers of assets. An entity was precluded from reflecting a tax benefit or expense from an intra-entity asset transfer between entities that file separate tax returns, whether or not such entities are in different tax jurisdictions, until the asset had been sold to a third party or otherwise recovered. The buyer of such asset was prohibited from recognizing a deferred tax asset for the temporary difference arising from the excess of the buyer’s tax basis over the cost to the seller. The adoption of this guidance had an immaterial impact on the Consolidated Financial Statements. On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to accounting for business combinations. This guidance clarifies the definition of a business for the purposes of evaluating whether a particular transaction should be accounted for as an acquisition or disposal of a business or an asset. Generally, a business is an integrated set of assets and activities that contain inputs, processes, and outputs, although outputs are not required. This guidance provides a “screen” to determine whether an integrated set of assets and activities qualifies as a business. If substantially all of the fair value of the gross assets is concentrated in a single identifiable asset or a group of similar identifiable assets, the definition of a business has not been met and the transaction should be accounted for as an acquisition or disposal of an asset. Otherwise, an entity is required to evaluate whether the integrated set of assets and activities include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create output and are no longer to consider whether a market participant could replace any missing elements. This guidance also narrows the definition of an output. Previously, an output was defined as the ability to provide a return in the form of dividends, lower costs, or other economic benefits directly to investors, owners, members, or participants. An output is now defined as the ability to provide goods or services to customers, investment income, or other revenues. The adoption of this guidance had no immediate impact on the Consolidated Financial Statements; however, this guidance will need to be considered in the event Alcoa Corporation acquires or disposes of an integrated set of assets and activities. On January 1, 2018, Alcoa Corporation early adopted guidance issued by the FASB to the assessment of goodwill for impairment as it relates to the quantitative test. Prior to this guidance, there were two steps when performing a quantitative impairment test. The first step required an entity to compare the current fair value of a reporting unit to its carrying value. In the event the reporting unit’s estimated fair value was less than its carrying value, an entity performed the second step, which was to compare the carrying amount of the reporting unit’s goodwill with the implied fair value of that goodwill. The implied fair value of goodwill is the excess of the fair value of the reporting unit over the fair value amounts assigned to all of the assets and liabilities of that unit as if the reporting unit was acquired in a business combination and the fair value of the reporting unit represented the purchase price. If the carrying value of goodwill exceeded its implied fair value, an impairment loss equal to such excess was recognized. This guidance eliminates the second step of the quantitative impairment test. Accordingly, an entity would recognize an impairment of goodwill for a reporting unit, if under what was previously referred to as the first step, the estimated fair value of the reporting unit is less than the carrying value. The impairment would be equal to the excess of the reporting unit’s carrying value over its fair value not to exceed the total amount of goodwill applicable to that reporting unit. The adoption of this guidance had no immediate impact on the Consolidated Financial Statements; however, this guidance will need to be considered each time the Company performs an assessment of goodwill for impairment under the quantitative test. On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to the presentation of net periodic benefit cost related to pension and other postretirement benefit plans. This guidance requires that an entity report the service cost component of net periodic benefit cost in the same line item(s) on its income statement as other compensation costs arising from services rendered by the pertinent employees during a reporting period. The other components of net periodic benefit cost (see Note J) are required to be reported separately from the service cost component. In other words, these other components may be aggregated and presented as a separate line item or they may be reported in existing line items on the income statement other than such line items that include the service cost component. Previously, Alcoa Corporation reported all components of net periodic benefit cost, except for certain settlements, curtailments, and special termination benefits, in Cost of goods sold (business employees) and Selling, general administrative, and other expenses (corporate employees) consistent with the location of other compensation costs related to the respective employees. The non-service non-service non-service non-service non-service non-service On January 1, 2018, Alcoa Corporation adopted guidance issued by the FASB to the accounting for stock-based compensation when there has been a modification to the terms or conditions of a share-based payment award. This guidance requires an entity to account for the modification only when there has been a substantive change to the terms or conditions of a share-based payment award. A substantive change occurs when the fair value, vesting conditions or balance sheet classification (liability or equity) of a share-based payment award is/are different immediately before and after the modification. Previously, an entity was required to account for any modification in the terms or conditions of a share-based payment award. The adoption of this guidance had no immediate impact on the Consolidated Financial Statements; however, this guidance will need to be considered if the Company initiates a modification that is determined to be a substantive change to an outstanding share-based award. Additionally, the Company will no longer account for any future non-substantive Issued In January 2018, the FASB issued guidance regarding the assessment of land easements (or rights of way) under the pending lease accounting requirements to be adopted on January 1, 2019 (see Recently Issued Accounting Guidance in Note B to the Consolidated Financial Statements in Part II Item 8 of Alcoa Corporation’s Annual Report on Form 10-K In February 2018, the FASB issued guidance regarding the reclassification of certain income tax effects reported in accumulated comprehensive income (loss) in response to U.S. tax legislation enacted on December 22, 2017 known as the U.S. Tax Cuts and Jobs Act of 2017 (the “TCJA”). For corporations, one of the main provisions of the TCJA was the reduction in the corporate income tax rate to 21% from 35%. Under current income tax accounting requirements, an entity was required to remeasure applicable U.S. deferred tax assets and deferred tax liabilities at the 21% tax rate effective on the TCJA enactment date. This remeasurement was required to be recognized in an entity’s income tax provision in its income statement. However, certain of these deferred tax assets and deferred tax liabilities relate to income tax effects initially recognized at the 35% tax rate through other comprehensive income (loss) on items reported within accumulated other comprehensive income (loss) on an entity’s balance sheet. Consequently, an entity’s financial statements will reflect an inconsistency between the deferred tax assets and deferred tax liabilities measured at 21% and the related income tax effects in accumulated other comprehensive income (loss) recorded at 35%. Accordingly, this guidance provides a one-time

Revenue

Revenue	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue	C. Revenue The Company measures revenue based on the consideration it expects to be entitled to receive in exchange for its products. The standard terms and conditions of customer orders and contracts include general rights of return and product warranty provisions related to nonconforming or “out-of-spec” product. Depending on the circumstances, the product is either replaced or a quality adjustment is issued. Historically, such returns and adjustments have not been material to Alcoa Corporation’s Consolidated Financial Statements. The Company considers shipping and handling activities as costs to fulfill the promise to transfer the related products. As a result, customer payments of shipping and handling costs are recorded as a component of revenue. Also, Alcoa Corporation may collect various taxes (e.g., sales, use, value-added, excise) from its customers related to the sale of its products and remit such amounts to governmental authorities. As such, amounts paid to the Company for these types of taxes are excluded from the transaction price used to determine the proper measurement of revenue. Alcoa Corporation has five product divisions as follows: Bauxite — Alumina — Primary aluminum — Flat-rolled aluminum — Energy — The following table represents the general commercial profile of the Company’s Bauxite, Alumina, Primary aluminum, and Flat-rolled aluminum product divisions (see text below table for Energy): Product division Pricing components Shipping terms (4) Payment terms (5) Bauxite Negotiated FOB/CIF LC Sight Alumina: Smelter-grade API (1) FOB LC Sight/CAD/Net 30 days Non-metallurgical Negotiated FOB/CIF Net 30 days Primary aluminum: Common alloy ingot LME + Regional premium (2) DAP/CIF Net 30 to 45 days Value-add ingot LME + Regional premium + Product (2) DAP/CIF Net 30 to 45 days Flat-rolled aluminum Metal + Conversion (3) DAP Negotiated (1) API (Alumina Price Index) is a pricing mechanism that is calculated by the Company based on the average of a prior month’s daily spot prices. (2) LME (London Metal Exchange) is a globally recognized exchange for commodity trading, including aluminum. The LME pricing component represents the underlying base metal component, based on quoted prices for aluminum on the exchange. The regional premium represents the incremental price over the base LME component that is associated with the physical delivery of metal to a particular region (e.g., the Midwest premium for metal sold in the United States). The product premium represents the incremental price for receiving physical metal in a particular shape (e.g., billet, rod, slab, etc.) or alloy. (3) Metal represents the underlying base metal component plus a regional premium – see footnote 2 above. Conversion represents the incremental price over the metal price component that is associated with converting primary or scrap aluminum into sheet. (4) CIF (cost, insurance, and freight) means that the Company pays for these items until the product reaches the buyer’s designated destination point related to transportation by vessel. DAP (delivered at place) means the same as CIF related to all methods of transportation. FOB (free on board) means that the Company pays for costs, insurance, and freight until the product reaches the seller’s designated shipping point. (5) The net number of days means that the customer is required to remit payment to the Company for the invoice amount within the designated number of days. LC Sight is a letter of credit that is payable immediately (usually within five to ten business days) after a seller meets the requirements of the letter of credit (i.e. shipping documents that evidence the seller performed its obligations as agreed to with a buyer). CAD (cash against documents) is a payment arrangement in which a seller instructs a bank to provide shipping and title documents to the buyer at the time the buyer pays in full the accompanying bill of exchange. For the Company’s Energy product division, sales of electricity are based on current market prices. Electricity is provided to customers on demand through a national or regional power grid; the customer simultaneously receives and consumes the electricity. Payment terms are generally within 10 days related to the previous 30 days of electricity consumption. The following table details Alcoa Corporation’s revenue by product division: First quarter ended March 31, 2018 2017 Primary aluminum $ 1,647 $ 1,352 Alumina 913 731 Flat-rolled aluminum 429 423 Energy 73 90 Bauxite 45 70 Other* (17 ) (11 ) $ 3,090 $ 2,655 * Other includes realized gains and losses related to embedded derivative instruments designated as cash flow hedges of forward sales of aluminum (see Note K).

Restructuring and Other Charges

Restructuring and Other Charges	3 Months Ended
	Mar. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring and Other Charges	D. Restructuring and Other Charges In the first quarter of 2017, Alcoa Corporation recorded Restructuring and other charges of $10, which were comprised of the following components: $13 for additional contract costs related to the curtailed Wenatchee smelter; $2 for miscellaneous items; and a reversal of $5 associated with layoff reserves related to prior periods. Alcoa Corporation does not include Restructuring and other charges in the results of its reportable segments. The impact of allocating such charges to segment results would have been as follows: First quarter ended March 31, 2018 2017 Bauxite $ — $ — Alumina (1 ) — Aluminum 5 12 Segment total 4 12 Corporate (23 ) (2 ) Total restructuring and other charges $ (19 ) $ 10 As of March 31, 2018, approximately 120 of the 140 employees associated with 2017 restructuring programs were separated. The remaining separations for the 2017 restructuring programs are expected to be completed by the end of 2018. In the 2018 first quarter, cash payments of $2 were made against layoff reserves related to 2017 restructuring programs. Activity and reserve balances for restructuring charges were as follows: Layoff costs Other costs Total Reserve balances at December 31, 2016 $ 38 $ 28 $ 66 2017: Cash payments (30 ) (43 ) (73 ) Restructuring charges 23 67 90 Other* (20 ) (18 ) (38 ) Reserve balances at December 31, 2017 11 34 45 2018: Cash payments (3 ) (7 ) (10 ) Restructuring charges — 4 4 Other* — — — Reserve balances at March 31, 2018 $ 8 $ 31 $ 39 * Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2017, Other for Layoff costs also included a reclassification of $8 in pension benefits costs, as these obligations were included in Alcoa Corporation’s separate liability for pension benefits obligations. Additionally in 2017, Other for Other costs also included a reclassification of the following restructuring charges: $10 in asset retirement and $8 in environmental obligations, as these liabilities were included in Alcoa Corporation’s separate reserves for asset retirement obligations and environmental remediation. The remaining reserves are expected to be paid in cash during the remainder of 2018, with the exception of $3, which relates to the termination of an office lease contract and is expected to be paid no later than the end of 2020.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Information	E. Segment Information Bauxite Alumina Aluminum Total First quarter ended March 31, 2018 Sales: Third-party sales $ 47 $ 914 $ 2,111 $ 3,072 Intersegment sales 249 454 4 707 Total sales $ 296 $ 1,368 $ 2,115 $ 3,779 Adjusted EBITDA $ 110 $ 392 $ 153 $ 655 Supplemental information: Depreciation, depletion, and amortization $ 29 $ 53 $ 106 $ 188 Equity loss — (1 ) — (1 ) First quarter ended March 31, 2017 Sales: Third-party sales $ 70 $ 734 $ 1,806 $ 2,610 Intersegment sales 219 361 4 584 Total sales $ 289 $ 1,095 $ 1,810 $ 3,194 Adjusted EBITDA $ 110 $ 297 $ 217 $ 624 Supplemental information: Depreciation, depletion, and amortization $ 18 $ 49 $ 101 $ 168 Equity income (loss) — 1 (7 ) (6 ) The following table reconciles total segment Adjusted EBITDA to consolidated net income attributable to Alcoa Corporation: First quarter ended March 31, 2018 2017 Total segment Adjusted EBITDA $ 655 $ 624 Unallocated amounts: Transformation (1),(2) (2 ) (20 ) Corporate inventory accounting (1),(3) 31 (17 ) Corporate expenses (4) (27 ) (33 ) Provision for depreciation, depletion, and amortization (194 ) (179 ) Restructuring and other charges (D) 19 (10 ) Interest expense (26 ) (26 ) Other (expenses) income, net (N) (21 ) 79 Other (1),(5) (23 ) — Consolidated income before income taxes 412 418 Provision for income taxes (138 ) (110 ) Net income attributable to noncontrolling interest (124 ) (83 ) Consolidated net income attributable to Alcoa Corporation $ 150 $ 225 (1) Effective in the first quarter of 2018, management elected to change the presentation of certain line items in the reconciliation of total segment Adjusted EBITDA to consolidated net income attributable to Alcoa Corporation to provide additional transparency to the nature of these reconciling items. Accordingly, Transformation (see footnote 2), which was previously reported within Other, is presented as a separate line item. Additionally, Impact of LIFO (last in, first out) and Metal price lag, which were previously reported as separate line items, are now combined and reported in a new line item labeled Corporate inventory accounting (see footnote 3). Also, the impact of intersegment profit eliminations, which was previously reported within Other, is reported in the new Corporate inventory accounting line item. The applicable information for the prior period presented was recast to reflect these changes. (2) Transformation includes, among other items, the Adjusted EBITDA of previously closed operations. (3) Corporate inventory accounting is composed of the impacts of LIFO inventory accounting, metal price lag, and intersegment profit eliminations. Metal price lag describes the timing difference created when the average price of metal sold differs from the average cost of the metal when purchased by Alcoa Corporation’s rolled aluminum operations. In general, when the price of metal increases, metal price lag is favorable, and when the price of metal decreases, metal price lag is unfavorable. (4) Corporate expenses are composed of general administrative and other expenses of operating the corporate headquarters and other global administrative facilities, as well as research and development expenses of the corporate technical center. (5) Other includes certain items that impact Cost of goods sold and Selling, general administrative, and other expenses on Alcoa Corporation’s Statement of Consolidated Operations that are not included in the Adjusted EBITDA of the reportable segments.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	F. Earnings Per Share The information used to compute basic and diluted EPS attributable to Alcoa Corporation common shareholders was as follows (shares in millions): First quarter ended March 31, 2018 2017 Net income attributable to Alcoa Corporation $ 150 $ 225 Average shares outstanding – basic 186 184 Effect of dilutive securities: Stock options 1 1 Stock and performance awards 1 1 Average shares outstanding – diluted 188 186 Options to purchase 1 million shares of common stock at a weighted average exercise price of $36.29 were outstanding as of March 31, 2017, but were not included in the computation of diluted EPS because they were anti-dilutive, as the exercise prices of the options were greater than the average market price of Alcoa Corporation’s common stock.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Accumulated Other Comprehensive Loss	G. Accumulated Other Comprehensive Loss The following table details the activity of the three components that comprise Accumulated other comprehensive loss for both Alcoa Corporation’s shareholders and noncontrolling interest: Alcoa Corporation Noncontrolling interest First quarter ended March 31, First quarter ended March 31, 2018 2017 2018 2017 Pension and other postretirement benefits (J) Balance at beginning of period $ (2,786 ) $ (2,330 ) $ (47 ) $ (56 ) Other comprehensive income (loss): Unrecognized net actuarial loss and prior service cost/benefit 75 (5 ) 1 (1 ) Tax (expense) benefit (8 ) 1 (1 ) — Total Other comprehensive income (loss) before reclassifications, net of tax 67 (4 ) — (1 ) Amortization of net actuarial loss and prior service cost/benefit (1) 36 50 1 — Tax expense (2) (2 ) (2 ) — — Total amount reclassified from Accumulated other comprehensive loss, net of tax (6) 34 48 1 — Total Other comprehensive income (loss) 101 44 1 (1 ) Balance at end of period $ (2,685 ) $ (2,286 ) $ (46 ) $ (57 ) Foreign currency translation Balance at beginning of period $ (1,467 ) $ (1,655 ) $ (581 ) $ (677 ) Other comprehensive income (loss) (3) 1 239 (14 ) 114 Balance at end of period $ (1,466 ) $ (1,416 ) $ (595 ) $ (563 ) Cash flow hedges (K) Balance at beginning of period $ (929 ) $ 210 $ 51 $ 1 Other comprehensive income (loss): Net change from periodic revaluations 635 (380 ) (20 ) 120 Tax (expense) benefit (99 ) 58 6 (36 ) Total Other comprehensive income (loss) before reclassifications, net of tax 536 (322 ) (14 ) 84 Net amount reclassified to earnings: Aluminum contracts (4) 27 18 — — Financial contracts (5) (13 ) (1 ) (9 ) (1 ) Foreign exchange contracts (4) (1 ) — — — Sub-total 13 17 (9 ) (1 ) Tax benefit (expense) (2) 1 (3 ) 3 — Total amount reclassified from Accumulated other comprehensive income (loss), net of tax (6) 14 14 (6 ) (1 ) Total Other comprehensive income (loss) 550 (308 ) (20 ) 83 Balance at end of period $ (379 ) $ (98 ) $ 31 $ 84 (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note J). (2) These amounts were reported in Provision for income taxes on the accompanying Statement of Consolidated Operations. (3) In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings. (4) These amounts were reported in Sales on the accompanying Statement of Consolidated Operations. (5) These amounts were reported in Cost of goods sold on the accompanying Statement of Consolidated Operations. (6) A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 5.

Investments

Investments	3 Months Ended
	Mar. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Investments	H. Investments First quarter ended March 31, 2018 2017 Sales $ 1,253 $ 916 Cost of goods sold 960 678 Net income 65 23

Inventories

Inventories	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Inventories	I. Inventories March 31, 2018 December 31, 2017 Finished goods $ 347 $ 296 Work-in-process 314 258 Bauxite and alumina 581 585 Purchased raw materials 551 473 Operating supplies 145 147 LIFO reserve (308 ) (306 ) $ 1,630 $ 1,453 At March 31, 2018 and December 31, 2017, the total amount of inventories valued on a LIFO basis was $561, or 29%, and $516, or 29%, respectively, of total inventories before LIFO adjustments. The inventory values, prior to the application of LIFO, are generally determined under the average cost method, which approximates current cost.

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits	J. Pension and Other Postretirement Benefits First quarter ended March 31, 2018 2017 Pension benefits Service cost $ 14 $ 18 Interest cost (1) 59 61 Expected return on plan assets (1) (90 ) (99 ) Recognized net actuarial loss (1) 55 46 Amortization of prior service cost (1) 2 2 Curtailments (2) 5 — Net periodic benefit cost $ 45 $ 28 (1) These amounts were reported in Other expenses (income), net on the accompanying Statement of Consolidated Operations (see Note B). (2) These amounts were reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations (see Note D). First quarter ended March 31, 2018 2017 Other postretirement benefits Service cost $ 1 $ 1 Interest cost (1) 9 9 Recognized net actuarial loss (1) 3 3 Amortization of prior service benefit (1) — (1 ) Curtailments (2) (28 ) — Net periodic benefit cost $ (15 ) $ 12 (1) These amounts were reported in Other expenses (income), net on the accompanying Statement of Consolidated Operations (see Note B). (2) These amounts were reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations (see Note D). Alcoa Corporation sponsors several defined benefit pension and other postretirement employee benefit plans, primarily in the United States and Canada. The pension benefit plans and the other postretirement benefit plans cover an aggregate of approximately 54,000 and approximately 48,000 participants, respectively. In January 2018, the Company communicated retirement benefit changes to certain U.S. and Canadian plan participants. Effective January 1, 2021, all U.S. and Canadian salaried employees that are participants in three of the Company’s defined benefit pension plans will cease accruing retirement benefits for future service. This change will affect approximately 800 employees, who will be transitioned to country-specific defined contribution plans, in which the Company will contribute 3% of these participants’ eligible earnings on an annual basis. Such contributions will be incremental to any employer savings match the employees may receive under existing defined contribution plans. Participants already collecting benefits under these defined benefit pension plans are not affected by these changes. This change resulted in the adoption of a significant plan amendment by the three pension benefit plans in January 2018. Accordingly, these plans were required to be remeasured, and through this process, the discount rate (weighted-average for these three plans) was updated from 3.65% at December 31, 2017 to 3.80% at January 31, 2018. The remeasurement of these plans resulted in a decrease of $57 to both Alcoa’s pension benefits liability and Accumulated other comprehensive loss. The remeasurement of these plans also resulted in a curtailment charge of $5 in the first quarter of 2018, representing prior service cost. This amount was reclassified to earnings through Restructuring and other charges from Accumulated other comprehensive loss. Also, effective January 1, 2021, Alcoa Corporation will no longer contribute to pre-Medicare

Derivatives and Other Financial

Derivatives and Other Financial Instruments	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Derivatives and Other Financial Instruments	K. Derivatives and Other Financial Instruments Fair Value Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy distinguishes between (i) market participant assumptions developed based on market data obtained from independent sources (observable inputs) and (ii) an entity’s own assumptions about market participant assumptions developed based on the best information available in the circumstances (unobservable inputs). The fair value hierarchy consists of three broad levels, which gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are described below: • Level 1 - Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. • Level 2 - Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly, including quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; inputs other than quoted prices that are observable for the asset or liability (e.g., interest rates); and inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 - Inputs that are both significant to the fair value measurement and unobservable. Derivatives Alcoa Corporation is exposed to certain risks relating to its ongoing business operations, including financial, market, political, and economic risks. The following discussion provides information regarding Alcoa Corporation’s exposure to the risks of changing commodity prices and foreign currency exchange rates. Alcoa Corporation’s commodity and derivative activities are subject to the management, direction, and control of the Strategic Risk Management Committee (SRMC), which consists of at least three members, including the chief executive officer and the chief financial officer. The remaining member(s) are other officers and/or employees of the Company as the chief executive officer may designate from time to time. Currently, the only other member of the SRMC is Alcoa Corporation’s treasurer. The SRMC meets on a periodic basis to review derivative positions and strategy and reports to the Audit Committee of Alcoa Corporation’s Board of Directors on the scope of its activities. Alcoa Corporation’s aluminum, energy, and foreign exchange contracts are held for purposes other than trading. They are used primarily to mitigate uncertainty and volatility, and to cover underlying exposures. Alcoa Corporation is not involved in trading activities for energy, weather derivatives, or other nonexchange commodity trading activities. Several of Alcoa Corporation’s aluminum, energy, and foreign exchange contracts are classified as Level 1 or Level 2 under the fair value hierarchy. The total fair value of these derivative contracts recorded as assets and liabilities was $27 and $48, respectively, at March 31, 2018 and $44 and $117, respectively, at December 31, 2017. In the first quarter of 2018 and 2017, Alcoa Corporation recognized a loss of $4 and $22, respectively, in Other expenses (income), net on the accompanying Statement of Consolidated Operations related to these contracts. Certain of these contracts are designated as either fair value or cash flow hedging instruments. For the contracts designated as cash flow hedges, Alcoa Corporation recognized an unrealized gain of $68 and an unrealized loss of $50 in Other comprehensive income (loss) in the first quarter of 2018 and 2017, respectively. In addition to the Level 1 and 2 derivative instruments described above, Alcoa Corporation has several derivative instruments classified as Level 3 under the fair value hierarchy. These instruments are composed of (i) embedded aluminum derivatives and an embedded credit derivative related to energy supply contracts and (ii) freestanding financial contracts related to energy purchases on the spot market, all of which are associated with nine smelters and three refineries. Certain of the embedded aluminum derivatives and financial contracts were designated as cash flow hedging instruments. All of these Level 3 derivative instruments are described below in detail and are enumerated as D1 through D11. The following section describes the valuation methodologies used by Alcoa Corporation to measure its Level 3 derivative instruments at fair value. Derivative instruments classified as Level 3 in the fair value hierarchy represent those in which management has used at least one significant unobservable input in the valuation model. Alcoa Corporation uses a discounted cash flow model to fair value all Level 3 derivative instruments. Where appropriate, the description below includes the key inputs to those models and any significant assumptions. These valuation models are reviewed and tested at least on an annual basis. Inputs in the valuation models for Level 3 derivative instruments are composed of the following: (i) quoted market prices (e.g., aluminum prices on the 10-year 10-year D1 through D5. 10-year D6. D7. LME-linked D8. D9. 30-year 30-year 30-year 30-year Ba/BB-rated (10-year) Ba/BB-rated (30-year) D10 and D11. In January 2017, Alcoa Corporation and the counterparty entered into a new financial contract (D11) to hedge the anticipated power requirements at this smelter for the period from August 2017 through July 2021 and amended the existing financial contract to both reduce the hedged amount of anticipated power requirements and to move up the effective termination date to July 31, 2017. The new financial contract has been designated as a cash flow hedge of future purchases of electricity. Unrealized gains and losses on the new financial contract were recorded in Other comprehensive income (loss) on the accompanying Consolidated Balance Sheet while realized gains and losses were recorded (began in August 2017) in Cost of goods sold as electricity purchases were made from the spot market. The following table presents quantitative information related to the significant unobservable inputs described above for Level 3 derivative contracts: Fair value at March 31, 2018 Unobservable input Range ($ in full amounts) Assets: Embedded aluminum derivative (D7) $ — Interrelationship of future aluminum and oil prices Aluminum: $1,991 per metric ton in April 2018 to $2,019 per metric ton in October 2018 Oil: $70 per barrel in January 2018 to $67 per barrel in October 2018 Financial contract (D11) 124 Interrelationship of forward energy price and the Consumer Price Index and price of electricity beyond forward curve Electricity: $65.43 per megawatt hour in 2018 to $53.88 per megawatt hour in 2021 Liabilities: Embedded aluminum derivative (D1) 281 Interrelationship of LME price to the amount of megawatt hours of energy needed to produce the forecasted metric tons of aluminum Aluminum: $1,991 per metric ton in 2018 to $2,368 per metric ton in 2027 Electricity: rate of 4 million megawatt hours per year Embedded aluminum derivatives (D3 through D5) 198 Price of aluminum beyond forward curve Aluminum: $2,408 per metric ton in 2028 to $2,476 per metric ton in 2029 (two contracts) and $2,771 per metric ton in 2036 (one contract) Midwest premium: $0.1900 per pound in 2018 to $0.1900 per pound in 2029 (two contracts) and 2036 (one contract) Embedded aluminum derivative (D8) 25 Interrelationship of LME price to the amount of megawatt hours of energy needed to produce the forecasted metric tons of aluminum Aluminum: $1,991 per metric ton in 2018 to $2,037 per metric ton in 2019 Midwest premium: $0.1900 per pound in 2018 to $0.1900 per pound in 2019 Electricity: rate of 2 million megawatt hours per year Embedded aluminum derivative (D2) 11 Interrelationship of LME price to overall energy price Aluminum: $2,110 per metric ton in 2018 to $2,061 per metric ton in 2019 Embedded credit derivative (D9) 16 Estimated spread between the respective 30-year 2.05% (30-year The fair values of Level 3 derivative instruments recorded as assets and liabilities in the accompanying Consolidated Balance Sheet were as follows: March 31, 2018 December 31, Asset Derivatives Derivatives designated as hedging instruments: Fair value of derivative contracts – current: Financial contract $ 46 $ 96 Fair value of derivative contracts – noncurrent: Financial contract 78 101 Total derivatives designated as hedging instruments $ 124 $ 197 Total Asset Derivatives $ 124 $ 197 Liability Derivatives Derivatives designated as hedging instruments: Fair value of derivative contracts – current: Embedded aluminum derivatives $ 67 $ 120 Fair value of derivative contracts – noncurrent: Embedded aluminum derivatives 423 992 Total derivatives designated as hedging instruments $ 490 $ 1,112 Derivatives not designated as hedging instruments: Fair value of derivative contracts – current: Embedded aluminum derivative $ 25 $ 28 Embedded credit derivative 3 4 Fair value of derivative contracts – noncurrent: Embedded aluminum derivative — 6 Embedded credit derivative 13 23 Total derivatives not designated as hedging instruments $ 41 $ 61 Total Liability Derivatives $ 531 $ 1,173 The following tables present a reconciliation of activity for Level 3 derivative contracts: Assets Liabilities First quarter ended March 31, 2018 Financial Embedded aluminum Embedded Opening balance – January 1, 2018 $ 197 $ 1,146 $ 27 Total gains or losses (realized and unrealized) included in: Sales — (25 ) — Cost of goods sold (22 ) — — Other expenses, net — (6 ) (11 ) Other comprehensive income (51 ) (597 ) — Purchases, sales, issuances, and settlements* — — — Transfers into and/or out of Level 3* — — — Other — (3 ) — Closing balance – March 31, 2018 $ 124 $ 515 $ 16 Change in unrealized gains or losses included in earnings for derivative contracts held at March 31, 2018: Sales $ — $ — $ — Cost of goods sold — — — Other expenses, net — (6 ) (11 ) * In the 2018 first quarter, there were no purchases, sales, issuances or settlements of Level 3 derivative instruments. Additionally, there were no transfers of derivative instruments into or out of Level 3. Derivatives Designated As Hedging Instruments – Cash Flow Hedges For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of unrealized gains or losses on the derivative is reported as a component of other comprehensive income. Realized gains or losses on the derivative are reclassified from other comprehensive income into earnings in the same period or periods during which the hedged transaction impacts earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized directly in earnings immediately. Alcoa Corporation has five Level 3 embedded aluminum derivatives and one Level 3 financial contract (through November 2016 – see D10 above) that have been designated as cash flow hedges as described below. Additionally, in January 2017, Alcoa Corporation entered into a new financial contract, which was designated as a cash flow hedging instrument and was classified as Level 3 under the fair value hierarchy (see D11 above), that replaced the existing financial contract in August 2017. Embedded aluminum derivatives (D1 through D5). LME-linked In the first quarter of 2018 and 2017, Alcoa Corporation recognized a net unrealized gain of $597 and a net unrealized loss of $498, respectively, in Other comprehensive income (loss) related to these five derivative instruments. Additionally, Alcoa Corporation reclassified a realized loss of $25 and $18 from Accumulated other comprehensive loss to Sales in the first quarter of 2018 and 2017, respectively. Assuming market rates remain constant with the rates at March 31, 2018, a realized loss of $67 is expected to be recognized in Sales over the next 12 months. There was no ineffectiveness related to these five derivative instruments in the first quarter of 2018 and 2017. Financial contracts (D10 and D11). In addition, in January 2017, Alcoa Corporation entered into a new financial contract that hedges the anticipated power requirements at this smelter for the period from August 2017 through July 2021 (see D11 above). At March 31, 2018 and December 31, 2017, this financial contract hedges forecasted electricity purchases of 8,199,576 and 8,805,456, respectively, megawatt hours. In the first quarter of 2018 and 2017, Alcoa Corporation recognized an unrealized loss of $51 and an unrealized gain of $169, respectively, in Other comprehensive income (loss). Additionally, Alcoa Corporation reclassified a realized gain of $22 in the 2018 first quarter from Accumulated other comprehensive loss to Cost of goods sold. Assuming market rates remain consistent with the rates at March 31, 2018, a realized gain of $46 is expected to be recognized in Cost of goods sold over the next 12 months. Additionally, Alcoa Corporation recognized a gain of $1 in Other income, net related to hedge ineffectiveness in the first quarter of 2017. There was no ineffectiveness related to this contract in the first quarter of 2018. Derivatives Not Designated As Hedging Instruments Alcoa Corporation has two Level 3 embedded aluminum derivatives (D7 and D8) and one Level 3 embedded credit derivative (D9) that do not qualify for hedge accounting treatment and one Level 3 financial contract for which management elected to discontinue hedge accounting treatment (see D10 above). As such, gains and losses related to the changes in fair value of these instruments are recorded directly in earnings. In the first quarter of 2018 and 2017, Alcoa Corporation recognized a gain of $17 and $25, respectively, in Other expenses (income), net, of which a gain of $6 and a loss of $14, respectively, related to the embedded aluminum derivatives, a gain of $11 and $5, respectively, related to the embedded credit derivative, and a gain of $34 (2017 first quarter) related to the financial contract. Material Limitations The disclosures with respect to commodity prices and foreign currency exchange risk do not consider the underlying commitments or anticipated transactions. If the underlying items were included in the analysis, the gains or losses on the futures contracts may be offset. Actual results will be determined by several factors that are not under Alcoa Corporation’s control and could vary significantly from those factors disclosed. Alcoa Corporation is exposed to credit loss in the event of nonperformance by counterparties on the above instruments, as well as credit or performance risk with respect to its hedged customers’ commitments. Although nonperformance is possible, Alcoa Corporation does not anticipate nonperformance by any of these parties. Contracts are with creditworthy counterparties and are further supported by cash, treasury bills, or irrevocable letters of credit issued by carefully chosen banks. In addition, various master netting arrangements are in place with counterparties to facilitate settlement of gains and losses on these contracts. Other Financial Instruments The carrying values and fair values of Alcoa Corporation’s other financial instruments were as follows: March 31, 2018 December 31, 2017 Carrying value Fair value Carrying value Fair value Cash and cash equivalents $ 1,196 $ 1,196 $ 1,358 $ 1,358 Restricted cash 7 7 7 7 Long-term debt due within one year 15 15 16 16 Long-term debt, less amount due within one year 1,445 1,574 1,388 1,555 The following methods were used to estimate the fair values of other financial instruments: Cash and cash equivalents and Restricted cash. Long-term debt due within one year and Long-term debt, less amount due within one year. non-public

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	L. Income Taxes one-time Based on management’s preliminary analysis of the TCJA, the Company recorded a $22 discrete income tax charge in its Consolidated Financial Statements for the year ended December 31, 2017. This amount was provisional in nature in accordance with guidance issued by the SEC under Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act See Note P to the Consolidated Financial Statements in Part II Item 8 of Alcoa Corporation’s Annual Report on Form 10-K

Contingencies and Commitments

Contingencies and Commitments	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Commitments	M. Contingencies and Commitments Contingencies Unless specifically described to the contrary, all matters within Note M are the full responsibility of Alcoa Corporation pursuant to the Separation and Distribution Agreement. Additionally, the Separation and Distribution Agreement provides for cross-indemnities between the Company and Arconic for claims subject to indemnification. Litigation Italy 148— In the meantime, as a result of the conclusion of the European Commission Matter in January 2016 (see Note R to the Consolidated Financial Statements in Part II Item 8 of Alcoa Corporation’s Annual Report on Form 10-K for the year ended December 31, 2017), ParentCo’s management modified its outlook with respect to a portion of the then-pending legal proceedings related to the drawback dispute. As such, a charge of $37 (€34) was recorded in Restructuring and other charges for the year ended December 31, 2015 to establish a partial reserve for this matter. In December 2017, through an agreement with the Energy Authority, Alcoa Corporation settled this matter for $18 (€15) (paid in January 2018). Accordingly, the Company recorded a reduction of $22 (€19) (the U.S. dollar amount reflects the effects of foreign currency movements since 2015) to its previously established reserve in Restructuring and other charges on the Statement of Consolidated Operations for the year ended December 31, 2017. In January 2018, subsequent to making the previously referenced payment, Alcoa Corporation and the respective state attorney in Italy filed a joint request with the Regional Administrative Court for Lombardy to have this matter formally dismissed. The parties have yet to receive notice of the court’s formal recognition of the dismissal request. Also in December 2017, as part of a separate but related agreement to the above, the Company agreed to transfer ownership of the Portovesme smelter (permanently closed in 2014) to Invitalia, which is an Italian government agency responsible for managing economic development. However, the Company will retain previously accrued asset retirement obligations related to ParentCo’s decision in 2014 to decommission the Portovesme smelter; such liabilities may be reduced upon Invitalia achieving certain milestones related to the future of the smelter. The carrying value of the assets related to the Portovesme site were previously written down to zero in 2014 as a direct result of this decision by ParentCo. Additionally, this agreement included a framework for the future settlement of a groundwater remediation project related to the Portovesme site (see Fusina and Portovesme, Italy in Environmental Matters below). In February 2018, the Company completed the transfer of ownership of the Portovesme smelter to Invitalia. Environmental Matters Alcoa Corporation participates in environmental assessments and cleanups at several locations. These include owned or operating facilities and adjoining properties, previously owned or operating facilities and adjoining properties, and waste sites, including Superfund (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)) sites. A liability is recorded for environmental remediation when a cleanup program becomes probable and the costs can be reasonably estimated. As assessments and cleanups proceed, the liability is adjusted based on progress made in determining the extent of remedial actions and related costs. The liability can change substantially due to factors such as, among others, the nature and extent of contamination, changes in remedial requirements, and technological changes. Alcoa Corporation’s remediation reserve balance was $284 and $294 at March 31, 2018 and December 31, 2017 (of which $50 and $36 was classified as a current liability), respectively, and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated. In the 2018 first quarter, the remediation reserve was increased by an immaterial amount. The changes to the remediation reserve were recorded in Cost of goods sold on the accompanying Statement of Consolidated Operations. Payments related to remediation expenses applied against the reserve were $6 in the 2018 first quarter. This amount includes expenditures currently mandated, as well as those not required by any regulatory authority or third party. In the 2018 first quarter, the change in the reserve also reflects both a decrease of $5 for the reclassification of a liability to Asset retirement obligations on Alcoa Corporation’s Consolidated Balance Sheet as of March 31, 2018 and an increase of $1 due to the effects of foreign currency translation. The Separation and Distribution Agreement includes provisions for the assignment or allocation of environmental liabilities between Alcoa Corporation and Arconic, including certain remediation obligations associated with environmental matters. In general, the respective parties are responsible for the environmental matters associated with their operations, and with the properties and other assets assigned to each. Additionally, the Separation and Distribution Agreement lists environmental matters with a shared responsibility between the two companies with an allocation of responsibility and the lead party responsible for management of each matter. For matters assigned to Alcoa Corporation and Arconic under the Separation and Distribution Agreement, the companies have agreed to indemnify each other in whole or in part for environmental liabilities arising from operations prior to the Separation Date. The following description provides details regarding the current status of certain significant reserves related to current or former Alcoa Corporation sites. With the exception of the Fusina, Italy matter, Alcoa Corporation assumed full responsibility of the matters described below. General— Sherwin, TX— Baie Comeau, Quebec, Canada— Fusina and Portovesme, Italy— For the Fusina site, Trasformazioni has a soil and groundwater remediation project, which was approved by the MOE through a final ministerial decree issued in August 2014. Additionally, under an administrative agreement reached in February 2014 with the MOE, Trasformazioni is required to make annual payments over a 10-year period for groundwater emergency containment and natural resource damages related to the Fusina site. Trasformazioni began work on the soil remediation project in October 2017 and expects to complete the project by the end of 2019. The MOE assumed the responsibility for the execution of the groundwater remediation/emergency containment in accordance with the February 2014 settlement agreement, as part of a regional effort by the MOE, and project work is slated to begin in 2019. At March 31, 2018 and December 31, 2017, the reserve balance associated with all of the foregoing Fusina-related matters (excluding a portion related to the rolling operations – see below) was $8. Effective with the Separation Transaction, Arconic retained the portion of Trasformazioni’s obligation related to the Fusina rolling operations. Specifically, under the Separation and Distribution Agreement, Trasformazioni, and with it the Fusina properties, were assigned to Alcoa Corporation. Fusina Rolling S.r.l., entered into a lease agreement for the portion of property that included the rolling operations. Pursuant to the Separation and Distribution Agreement, the liabilities at Fusina described above were allocated between Alcoa Corporation (Trasformazioni) and Arconic (Fusina Rolling S.r.l.). For the Portovesme site, Trasformazioni has a soil remediation project, which was approved by the MOE through a final ministerial decree issued in October 2015. Project work on the soil remediation project commenced in mid-2016 and is expected to be completed in 2019. Additionally, Trasformazioni, along with four other entities that operated in the same industrial park, have submitted a groundwater remediation project, which was preliminarily approved in 2010 by the MOE. Since that time, the parties have performed additional studies and work to be incorporated into the final remedial design. In December 2017, a framework for the future settlement of the groundwater remediation project was included within an agreement to transfer the ownership of the Portovesme smelter to an Italian government agency (see Italy 148 in Litigation above). The MOE has confirmed its acceptance of the proposal set out in the framework; however, the total cost of the groundwater remediation project will not be determined until the final remedial design is completed in late 2018. The ultimate outcome of this matter may result in a change to the existing reserve for Portovesme. At March 31, 2018 and December 31, 2017, the reserve balance associated with all of the foregoing Portovesme-related matters was $15 and $16, respectively. Mosjøen, Norway— East St. Louis, IL— Tax Spain— In January 2017, Spain’s National Court issued a decision in favor of the Spanish consolidated tax group related to a similar assessment for the 2003 through 2005 tax years, effectively making that assessment null and void. Additionally, in August 2017, in lieu of receiving a formal assessment, the Company and Arconic reached a settlement with Spain’s tax authorities for the 2010 through 2013 tax years that had been under audit for a similar matter. Alcoa Corporation’s share of this settlement was not material to the Company’s Consolidated Financial Statements. Due to certain underlying technicalities, the ultimate outcomes related to the 2003 through 2005 and the 2010 through 2013 tax years are not indicative of the potential ultimate outcome of the assessment for the 2006 through 2009 tax years. The Company believes it has meritorious arguments to support the former Spanish consolidated tax group’s tax position and intends to vigorously litigate the remaining assessment through Spain’s court system. However, in the event the Company is unsuccessful, a portion of this assessment may be offset with existing tax loss carryforwards available to the Spanish consolidated tax group, which would be shared between the Company and Arconic pursuant to the Tax Matters Agreement related to the Separation Transaction. Additionally, it is possible that the Company may receive similar assessments for tax years subsequent to 2013. At this time, the Company is unable to reasonably predict the ultimate outcome for this matter. Brazil (AWAB)— Other On January 11, 2016, Sherwin Alumina Company, LLC (“Sherwin”), the current owner of a refinery previously owned by ParentCo (see below), and one of its affiliate entities, filed bankruptcy petitions in Corpus Christi, Texas for reorganization under Chapter 11 of the U.S. Bankruptcy Code. Sherwin informed the bankruptcy court that it intends to cease operations because it is not able to continue its bauxite supply agreement. On November 23, 2016, the bankruptcy court approved Sherwin’s plans for cessation of its operations. On February 16, 2017, Sherwin filed a bankruptcy Chapter 11 Plan (the “Plan”) and, on February 17, 2017, the court approved that Plan. In 2000, ParentCo acquired Reynolds Metals Company (“Reynolds,” a subsidiary of Alcoa Corporation), which included an alumina refinery in Gregory, Texas. As a condition of the Reynolds acquisition, ParentCo was required to divest this alumina refinery. In accordance with the terms of the divestiture in 2000, ParentCo agreed to retain responsibility for certain environmental obligations (see Environmental Matters above) and assigned to the buyer an Energy Services Agreement (“ESA”) with Gregory Power Partners (“Gregory Power”) for purchase of steam and electricity by the refinery. Through the bankruptcy proceedings, the owner of Sherwin exercised its right under the U.S. Bankruptcy Code to reject the agreement from 2000 containing the previously mentioned retained responsibility, which had the effect of terminating all rights and responsibilities of the parties to the agreement. As a result of Sherwin’s initial bankruptcy filing, separate legal actions were initiated against Reynolds by Gregory Power and Sherwin as follows. Gregory Power— pre-trial Sherwin — General In addition to the matters discussed above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Alcoa Corporation, including those pertaining to environmental, product liability, safety and health, contract dispute, and tax matters, and other actions and claims arising out of the normal course of business. While the amounts claimed in these other matters may be substantial, the ultimate liability is not readily determinable because of the considerable uncertainties that exist. Accordingly, it is possible that the Company’s liquidity or results of operations in a particular period could be materially affected by one or more of these other matters. However, based on facts currently available, management believes that the disposition of these other matters that are pending or asserted will not have a material adverse effect, individually or in the aggregate, on the financial position of the Company. Commitments Investments Alcoa Corporation has an investment in a joint venture related to the ownership and operation of an integrated aluminum complex (bauxite mine, alumina refinery, aluminum smelter, and rolling mill) in Saudi Arabia. The joint venture is owned 74.9% by the Saudi Arabian Mining Company (known as “Ma’aden”) and 25.1% by Alcoa Corporation and consists of three separate companies as follows: one each for the mine and refinery, the smelter, and the rolling mill. Alcoa Corporation accounts for its investment in the joint venture under the equity method. As of March 31, 2018 and December 31, 2017, the carrying value of Alcoa Corporation’s investment in this joint venture was $885 and $887, respectively. Capital investment in the project is expected to total approximately $10,800 (SAR 40.5 billion) and has been funded through a combination of equity contributions by the joint venture partners and project financing obtained by the joint venture companies, which has been partially guaranteed by both partners (see below). Both the equity contributions and the guarantees of the project financing are based on the joint venture’s partners’ ownership interests. Originally, it was estimated that Alcoa Corporation’s total equity contribution in the joint venture related to the capital investment in the project would be approximately $1,100, of which Alcoa Corporation has contributed $982. Based on changes to both the project’s capital investment and equity and debt structure from the initial plans, the estimated $1,100 equity contribution may be reduced. Separate from the capital investment in the project, Alcoa Corporation contributed $66 (Ma’aden contributed $199) to the joint venture in 2017 for short-term funding purposes in accordance with the terms of the joint venture companies’ financing arrangements. Both partners may be required to make such additional contributions in future periods. The rolling mill and mining and refining companies have project financing totaling $3,308 (reflects principal repayments made through March 31, 2018), of which a combined $830 represents Alcoa Corporation’s and AWAC’s respective 25.1% interest in the rolling mill company and the mining and refining company. Alcoa Corporation, itself and on behalf of AWAC, has issued guarantees (see below) to the lenders in the event of default on the debt service requirements by the rolling mill company through 2018 and 2021 and by the mining and refining company through 2019 and 2024 (Ma’aden issued similar guarantees related to its 74.9% interest). Alcoa Corporation’s guarantees for the rolling mill and mining and refining companies cover total debt service requirements of $122 in principal and up to a maximum of approximately $35 in interest per year (based on projected interest rates). Previously, Alcoa Corporation issued similar guarantees related to the project financing of the smelting company. In December 2017, the smelting company refinanced and/or amended all of its existing outstanding debt. The guarantees that were previously required of the Company were effectively terminated. At March 31, 2018 and December 31, 2017, the combined fair value of the guarantees was $3, which was included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. In the event Alcoa Corporation would be required to make payments under the guarantees related to the mining and refining company, 40% of such amount would be contributed to Alcoa Corporation by Alumina Limited, consistent with its ownership interest in AWAC. As a result of the Separation Transaction, the various lenders to the joint venture companies required Arconic to maintain joint and several guarantees with Alcoa Corporation. In the event of default by any of the joint venture companies, the lenders would make a claim against both Alcoa Corporation and Arconic. Accordingly, Alcoa Corporation would perform under its guarantee; however, if the Company failed to perform, Arconic would be required to perform under its own guarantee. Arconic would then subsequently seek indemnification from Alcoa Corporation under the terms of the Separation and Distribution Agreement.

Other Expenses (Income), Net

Other Expenses (Income), Net	3 Months Ended
	Mar. 31, 2018
Other Income and Expenses [Abstract]
Other Expenses (Income), Net	N. Other Expenses (Income), Net First quarter ended March 31, 2018 2017 Equity loss $ 2 $ 7 Foreign currency losses, net 3 16 Net gain from asset sales (5 ) (120 ) Net gain on mark-to-market (17 ) (3 ) Non-service 38 21 $ 21 $ (79 ) In the 2017 first quarter, Net gain from asset sales included a $120 gain related to the sale of certain energy operations in the United States.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	O. Subsequent Events On April 3, 2018, Alcoa Corporation signed group annuity contracts to transfer the obligation to pay the remaining retirement benefits of approximately 2,100 retirees from two Canadian defined benefit pension plans to three insurance companies. The transfer of approximately $555 in both plan obligations and plan assets, as well as a transaction fee of $25, was completed on April 13, 2018. The Company contributed approximately $95 between the two plans to facilitate the transaction and maintain the funding level of the remaining plan obligations. Prior to this transaction, these two Canadian pension plans combined had approximately 3,500 participants. In connection with this transaction, the Company will record a non-cash after-tax,

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	A. Basis of Presentation year-end 10-Q 10-K References in these Notes to “ParentCo” refer to Alcoa Inc., a Pennsylvania corporation, and its consolidated subsidiaries (through October 31, 2016, at which time was renamed Arconic Inc. (Arconic)). On November 1, 2016 (the “Separation Date”), ParentCo separated into two standalone, publicly-traded companies, Alcoa Corporation and Arconic (the “Separation Transaction”). In connection with the Separation Transaction, as of October 31, 2016, the Company and Arconic entered into several agreements to effect the Separation Transaction, including a Separation and Distribution Agreement and a Tax Matters Agreement. See Note A to the Consolidated Financial Statements in Part II Item 8 of Alcoa Corporation’s Annual Report on Form 10-K
Principles of Consolidation	Principles of Consolidation. AWAC is an unincorporated global joint venture between Alcoa Corporation and Alumina Limited and consists of several affiliated operating entities, which own, or have an interest in, or operate the bauxite mines and alumina refineries within Alcoa Corporation’s Bauxite and Alumina segments (except for the Poços de Caldas mine and refinery and a portion of the São Luís refinery, all in Brazil) and the Portland smelter in Australia. Alcoa Corporation owns 60% and Alumina Limited owns 40% of these individual entities, which are consolidated by the Company for financial reporting purposes and include Alcoa of Australia Limited, Alcoa World Alumina LLC (AWA), and Alcoa World Alumina Brasil Ltda. (AWAB). Alumina Limited’s interest in the equity of such entities is reflected as Noncontrolling interest on the accompanying Consolidated Balance Sheet.

Recently Adopted and Recently23

Recently Adopted and Recently Issued Accounting Guidance (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Summary of Cash and Cash Equivalents and Restricted Cash	The following table provides a reconciliation of Cash and cash equivalents and Restricted cash reported in the accompanying Consolidated Balance Sheet that sum to the Cash and cash equivalents and restricted cash at both the beginning of year and end of period presented on the accompanying Statement of Consolidated Cash Flows for the three months ended March 31, 2018: March 31, 2018 December 31, 2017 Cash and cash equivalents $ 1,196 $ 1,358 Restricted cash* 7 7 $ 1,203 $ 1,365 * These amounts are reported in Prepaid expenses and other current assets on the accompanying Consolidated Balance Sheet.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Product Division Information	The following table represents the general commercial profile of the Company’s Bauxite, Alumina, Primary aluminum, and Flat-rolled aluminum product divisions (see text below table for Energy): Product division Pricing components Shipping terms (4) Payment terms (5) Bauxite Negotiated FOB/CIF LC Sight Alumina: Smelter-grade API (1) FOB LC Sight/CAD/Net 30 days Non-metallurgical Negotiated FOB/CIF Net 30 days Primary aluminum: Common alloy ingot LME + Regional premium (2) DAP/CIF Net 30 to 45 days Value-add ingot LME + Regional premium + Product (2) DAP/CIF Net 30 to 45 days Flat-rolled aluminum Metal + Conversion (3) DAP Negotiated (1) API (Alumina Price Index) is a pricing mechanism that is calculated by the Company based on the average of a prior month’s daily spot prices. (2) LME (London Metal Exchange) is a globally recognized exchange for commodity trading, including aluminum. The LME pricing component represents the underlying base metal component, based on quoted prices for aluminum on the exchange. The regional premium represents the incremental price over the base LME component that is associated with the physical delivery of metal to a particular region (e.g., the Midwest premium for metal sold in the United States). The product premium represents the incremental price for receiving physical metal in a particular shape (e.g., billet, rod, slab, etc.) or alloy. (3) Metal represents the underlying base metal component plus a regional premium – see footnote 2 above. Conversion represents the incremental price over the metal price component that is associated with converting primary or scrap aluminum into sheet. (4) CIF (cost, insurance, and freight) means that the Company pays for these items until the product reaches the buyer’s designated destination point related to transportation by vessel. DAP (delivered at place) means the same as CIF related to all methods of transportation. FOB (free on board) means that the Company pays for costs, insurance, and freight until the product reaches the seller’s designated shipping point. (5) The net number of days means that the customer is required to remit payment to the Company for the invoice amount within the designated number of days. LC Sight is a letter of credit that is payable immediately (usually within five to ten business days) after a seller meets the requirements of the letter of credit (i.e. shipping documents that evidence the seller performed its obligations as agreed to with a buyer). CAD (cash against documents) is a payment arrangement in which a seller instructs a bank to provide shipping and title documents to the buyer at the time the buyer pays in full the accompanying bill of exchange.
Schedule of Revenue by Product Division	The following table details Alcoa Corporation’s revenue by product division: First quarter ended March 31, 2018 2017 Primary aluminum $ 1,647 $ 1,352 Alumina 913 731 Flat-rolled aluminum 429 423 Energy 73 90 Bauxite 45 70 Other* (17 ) (11 ) $ 3,090 $ 2,655 * Other includes realized gains and losses related to embedded derivative instruments designated as cash flow hedges of forward sales of aluminum (see Note K).

Restructuring and Other Charg25

Restructuring and Other Charges (Tables)	3 Months Ended
	Mar. 31, 2018
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Other Charges by Reportable Segments, Pretax	Alcoa Corporation does not include Restructuring and other charges in the results of its reportable segments. The impact of allocating such charges to segment results would have been as follows: First quarter ended March 31, 2018 2017 Bauxite $ — $ — Alumina (1 ) — Aluminum 5 12 Segment total 4 12 Corporate (23 ) (2 ) Total restructuring and other charges $ (19 ) $ 10
Activity and Reserve Balances for Restructuring Charges	Activity and reserve balances for restructuring charges were as follows: Layoff costs Other costs Total Reserve balances at December 31, 2016 $ 38 $ 28 $ 66 2017: Cash payments (30 ) (43 ) (73 ) Restructuring charges 23 67 90 Other* (20 ) (18 ) (38 ) Reserve balances at December 31, 2017 11 34 45 2018: Cash payments (3 ) (7 ) (10 ) Restructuring charges — 4 4 Other* — — — Reserve balances at March 31, 2018 $ 8 $ 31 $ 39 * Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2017, Other for Layoff costs also included a reclassification of $8 in pension benefits costs, as these obligations were included in Alcoa Corporation’s separate liability for pension benefits obligations. Additionally in 2017, Other for Other costs also included a reclassification of the following restructuring charges: $10 in asset retirement and $8 in environmental obligations, as these liabilities were included in Alcoa Corporation’s separate reserves for asset retirement obligations and environmental remediation.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Schedule of Operating Results,Capital Expenditures and Assets of Alcoa's Reportable Segments	The operating results of Alcoa Corporation’s reportable segments were as follows (differences between segment totals and consolidated amounts are in Corporate): Bauxite Alumina Aluminum Total First quarter ended March 31, 2018 Sales: Third-party sales $ 47 $ 914 $ 2,111 $ 3,072 Intersegment sales 249 454 4 707 Total sales $ 296 $ 1,368 $ 2,115 $ 3,779 Adjusted EBITDA $ 110 $ 392 $ 153 $ 655 Supplemental information: Depreciation, depletion, and amortization $ 29 $ 53 $ 106 $ 188 Equity loss — (1 ) — (1 ) First quarter ended March 31, 2017 Sales: Third-party sales $ 70 $ 734 $ 1,806 $ 2,610 Intersegment sales 219 361 4 584 Total sales $ 289 $ 1,095 $ 1,810 $ 3,194 Adjusted EBITDA $ 110 $ 297 $ 217 $ 624 Supplemental information: Depreciation, depletion, and amortization $ 18 $ 49 $ 101 $ 168 Equity income (loss) — 1 (7 ) (6 )
Schedule of Segment Adjusted EBITDA to Consolidated Net Income Attributable to Alcoa Corporation	The following table reconciles total segment Adjusted EBITDA to consolidated net income attributable to Alcoa Corporation: First quarter ended March 31, 2018 2017 Total segment Adjusted EBITDA $ 655 $ 624 Unallocated amounts: Transformation (1),(2) (2 ) (20 ) Corporate inventory accounting (1),(3) 31 (17 ) Corporate expenses (4) (27 ) (33 ) Provision for depreciation, depletion, and amortization (194 ) (179 ) Restructuring and other charges (D) 19 (10 ) Interest expense (26 ) (26 ) Other (expenses) income, net (N) (21 ) 79 Other (1),(5) (23 ) — Consolidated income before income taxes 412 418 Provision for income taxes (138 ) (110 ) Net income attributable to noncontrolling interest (124 ) (83 ) Consolidated net income attributable to Alcoa Corporation $ 150 $ 225 (1) Effective in the first quarter of 2018, management elected to change the presentation of certain line items in the reconciliation of total segment Adjusted EBITDA to consolidated net income attributable to Alcoa Corporation to provide additional transparency to the nature of these reconciling items. Accordingly, Transformation (see footnote 2), which was previously reported within Other, is presented as a separate line item. Additionally, Impact of LIFO (last in, first out) and Metal price lag, which were previously reported as separate line items, are now combined and reported in a new line item labeled Corporate inventory accounting (see footnote 3). Also, the impact of intersegment profit eliminations, which was previously reported within Other, is reported in the new Corporate inventory accounting line item. The applicable information for the prior period presented was recast to reflect these changes. (2) Transformation includes, among other items, the Adjusted EBITDA of previously closed operations. (3) Corporate inventory accounting is composed of the impacts of LIFO inventory accounting, metal price lag, and intersegment profit eliminations. Metal price lag describes the timing difference created when the average price of metal sold differs from the average cost of the metal when purchased by Alcoa Corporation’s rolled aluminum operations. In general, when the price of metal increases, metal price lag is favorable, and when the price of metal decreases, metal price lag is unfavorable. (4) Corporate expenses are composed of general administrative and other expenses of operating the corporate headquarters and other global administrative facilities, as well as research and development expenses of the corporate technical center. (5) Other includes certain items that impact Cost of goods sold and Selling, general administrative, and other expenses on Alcoa Corporation’s Statement of Consolidated Operations that are not included in the Adjusted EBITDA of the reportable segments.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted EPS Attributable to Alcoa Corporation Common Shareholders	The information used to compute basic and diluted EPS attributable to Alcoa Corporation common shareholders was as follows (shares in millions): First quarter ended March 31, 2018 2017 Net income attributable to Alcoa Corporation $ 150 $ 225 Average shares outstanding – basic 186 184 Effect of dilutive securities: Stock options 1 1 Stock and performance awards 1 1 Average shares outstanding – diluted 188 186

Accumulated Other Comprehensi28

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component	The following table details the activity of the three components that comprise Accumulated other comprehensive loss for both Alcoa Corporation’s shareholders and noncontrolling interest: Alcoa Corporation Noncontrolling interest First quarter ended March 31, First quarter ended March 31, 2018 2017 2018 2017 Pension and other postretirement benefits (J) Balance at beginning of period $ (2,786 ) $ (2,330 ) $ (47 ) $ (56 ) Other comprehensive income (loss): Unrecognized net actuarial loss and prior service cost/benefit 75 (5 ) 1 (1 ) Tax (expense) benefit (8 ) 1 (1 ) — Total Other comprehensive income (loss) before reclassifications, net of tax 67 (4 ) — (1 ) Amortization of net actuarial loss and prior service cost/benefit (1) 36 50 1 — Tax expense (2) (2 ) (2 ) — — Total amount reclassified from Accumulated other comprehensive loss, net of tax (6) 34 48 1 — Total Other comprehensive income (loss) 101 44 1 (1 ) Balance at end of period $ (2,685 ) $ (2,286 ) $ (46 ) $ (57 ) Foreign currency translation Balance at beginning of period $ (1,467 ) $ (1,655 ) $ (581 ) $ (677 ) Other comprehensive income (loss) (3) 1 239 (14 ) 114 Balance at end of period $ (1,466 ) $ (1,416 ) $ (595 ) $ (563 ) Cash flow hedges (K) Balance at beginning of period $ (929 ) $ 210 $ 51 $ 1 Other comprehensive income (loss): Net change from periodic revaluations 635 (380 ) (20 ) 120 Tax (expense) benefit (99 ) 58 6 (36 ) Total Other comprehensive income (loss) before reclassifications, net of tax 536 (322 ) (14 ) 84 Net amount reclassified to earnings: Aluminum contracts (4) 27 18 — — Financial contracts (5) (13 ) (1 ) (9 ) (1 ) Foreign exchange contracts (4) (1 ) — — — Sub-total 13 17 (9 ) (1 ) Tax benefit (expense) (2) 1 (3 ) 3 — Total amount reclassified from Accumulated other comprehensive income (loss), net of tax (6) 14 14 (6 ) (1 ) Total Other comprehensive income (loss) 550 (308 ) (20 ) 83 Balance at end of period $ (379 ) $ (98 ) $ 31 $ 84 (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note J). (2) These amounts were reported in Provision for income taxes on the accompanying Statement of Consolidated Operations. (3) In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings. (4) These amounts were reported in Sales on the accompanying Statement of Consolidated Operations. (5) These amounts were reported in Cost of goods sold on the accompanying Statement of Consolidated Operations. (6) A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 5.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments	A summary of unaudited financial information for Alcoa Corporation’s equity investments is as follows (amounts represent 100% of investee financial information): First quarter ended March 31, 2018 2017 Sales $ 1,253 $ 916 Cost of goods sold 960 678 Net income 65 23

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Inventory Components	March 31, 2018 December 31, 2017 Finished goods $ 347 $ 296 Work-in-process 314 258 Bauxite and alumina 581 585 Purchased raw materials 551 473 Operating supplies 145 147 LIFO reserve (308 ) (306 ) $ 1,630 $ 1,453

Pension and Other Postretirem31

Pension and Other Postretirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	The components of net periodic benefit cost were as follows: First quarter ended March 31, 2018 2017 Pension benefits Service cost $ 14 $ 18 Interest cost (1) 59 61 Expected return on plan assets (1) (90 ) (99 ) Recognized net actuarial loss (1) 55 46 Amortization of prior service cost (1) 2 2 Curtailments (2) 5 — Net periodic benefit cost $ 45 $ 28 (1) These amounts were reported in Other expenses (income), net on the accompanying Statement of Consolidated Operations (see Note B). (2) These amounts were reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations (see Note D). First quarter ended March 31, 2018 2017 Other postretirement benefits Service cost $ 1 $ 1 Interest cost (1) 9 9 Recognized net actuarial loss (1) 3 3 Amortization of prior service benefit (1) — (1 ) Curtailments (2) (28 ) — Net periodic benefit cost $ (15 ) $ 12 (1) These amounts were reported in Other expenses (income), net on the accompanying Statement of Consolidated Operations (see Note B). (2) These amounts were reported in Restructuring and other charges on the accompanying Statement of Consolidated Operations (see Note D).

Derivatives and Other Financi32

Derivatives and Other Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Quantitative Information for Level 3 Derivative Contracts	The following table presents quantitative information related to the significant unobservable inputs described above for Level 3 derivative contracts: Fair value at March 31, 2018 Unobservable input Range ($ in full amounts) Assets: Embedded aluminum derivative (D7) $ — Interrelationship of future aluminum and oil prices Aluminum: $1,991 per metric ton in April 2018 to $2,019 per metric ton in October 2018 Oil: $70 per barrel in January 2018 to $67 per barrel in October 2018 Financial contract (D11) 124 Interrelationship of forward energy price and the Consumer Price Index and price of electricity beyond forward curve Electricity: $65.43 per megawatt hour in 2018 to $53.88 per megawatt hour in 2021 Liabilities: Embedded aluminum derivative (D1) 281 Interrelationship of LME price to the amount of megawatt hours of energy needed to produce the forecasted metric tons of aluminum Aluminum: $1,991 per metric ton in 2018 to $2,368 per metric ton in 2027 Electricity: rate of 4 million megawatt hours per year Embedded aluminum derivatives (D3 through D5) 198 Price of aluminum beyond forward curve Aluminum: $2,408 per metric ton in 2028 to $2,476 per metric ton in 2029 (two contracts) and $2,771 per metric ton in 2036 (one contract) Midwest premium: $0.1900 per pound in 2018 to $0.1900 per pound in 2029 (two contracts) and 2036 (one contract) Embedded aluminum derivative (D8) 25 Interrelationship of LME price to the amount of megawatt hours of energy needed to produce the forecasted metric tons of aluminum Aluminum: $1,991 per metric ton in 2018 to $2,037 per metric ton in 2019 Midwest premium: $0.1900 per pound in 2018 to $0.1900 per pound in 2019 Electricity: rate of 2 million megawatt hours per year Embedded aluminum derivative (D2) 11 Interrelationship of LME price to overall energy price Aluminum: $2,110 per metric ton in 2018 to $2,061 per metric ton in 2019 Embedded credit derivative (D9) 16 Estimated spread between the respective 30-year 2.05% (30-year
Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities	The fair values of Level 3 derivative instruments recorded as assets and liabilities in the accompanying Consolidated Balance Sheet were as follows: March 31, 2018 December 31, Asset Derivatives Derivatives designated as hedging instruments: Fair value of derivative contracts – current: Financial contract $ 46 $ 96 Fair value of derivative contracts – noncurrent: Financial contract 78 101 Total derivatives designated as hedging instruments $ 124 $ 197 Total Asset Derivatives $ 124 $ 197 Liability Derivatives Derivatives designated as hedging instruments: Fair value of derivative contracts – current: Embedded aluminum derivatives $ 67 $ 120 Fair value of derivative contracts – noncurrent: Embedded aluminum derivatives 423 992 Total derivatives designated as hedging instruments $ 490 $ 1,112 Derivatives not designated as hedging instruments: Fair value of derivative contracts – current: Embedded aluminum derivative $ 25 $ 28 Embedded credit derivative 3 4 Fair value of derivative contracts – noncurrent: Embedded aluminum derivative — 6 Embedded credit derivative 13 23 Total derivatives not designated as hedging instruments $ 41 $ 61 Total Liability Derivatives $ 531 $ 1,173
Schedule of Reconciliation of Activity for Derivative Contracts	The following tables present a reconciliation of activity for Level 3 derivative contracts: Assets Liabilities First quarter ended March 31, 2018 Financial Embedded aluminum Embedded Opening balance – January 1, 2018 $ 197 $ 1,146 $ 27 Total gains or losses (realized and unrealized) included in: Sales — (25 ) — Cost of goods sold (22 ) — — Other expenses, net — (6 ) (11 ) Other comprehensive income (51 ) (597 ) — Purchases, sales, issuances, and settlements* — — — Transfers into and/or out of Level 3* — — — Other — (3 ) — Closing balance – March 31, 2018 $ 124 $ 515 $ 16 Change in unrealized gains or losses included in earnings for derivative contracts held at March 31, 2018: Sales $ — $ — $ — Cost of goods sold — — — Other expenses, net — (6 ) (11 ) * In the 2018 first quarter, there were no purchases, sales, issuances or settlements of Level 3 derivative instruments. Additionally, there were no transfers of derivative instruments into or out of Level 3.
Schedule of Reconciliation of Activity for Derivative Contracts	The carrying values and fair values of Alcoa Corporation’s other financial instruments were as follows: March 31, 2018 December 31, 2017 Carrying value Fair value Carrying value Fair value Cash and cash equivalents $ 1,196 $ 1,196 $ 1,358 $ 1,358 Restricted cash 7 7 7 7 Long-term debt due within one year 15 15 16 16 Long-term debt, less amount due within one year 1,445 1,574 1,388 1,555

Other Expenses (Income), Net (T

Other Expenses (Income), Net (Tables)	3 Months Ended
	Mar. 31, 2018
Other Income and Expenses [Abstract]
Schedule of Other Expenses (Income), Net	First quarter ended March 31, 2018 2017 Equity loss $ 2 $ 7 Foreign currency losses, net 3 16 Net gain from asset sales (5 ) (120 ) Net gain on mark-to-market (17 ) (3 ) Non-service 38 21 $ 21 $ (79 )

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail)	Mar. 31, 2018
Alumina Limited [Member]
Basis Of Presentation [Line Items]
Non-controlling interest, ownership percentage	40.00%
Alcoa Corporation [Member]
Basis Of Presentation [Line Items]
Ownership interest percentage	60.00%

Recently Adopted and Recently35

Recently Adopted and Recently Issued Accounting Guidance - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018	Jan. 01, 2017
Recently Issued Accounting Standards [Line Items]
Restricted cash	$ 7		$ 7
Cash (used for) provided from investing activities	(74)	$ 142
Net change in cash and cash equivalents and restricted cash	(162)	(37)
Cost of goods sold	2,381	2,023
Selling, general administrative, and other expenses	$ 67	71
Corporate income tax rate	21.00%		35.00%
Accounting Standards Update 2017-07 [Member]
Recently Issued Accounting Standards [Line Items]
Non-service cost components in other expenses, net	$ 38
Cost of goods sold		20
Selling, general administrative, and other expenses		1
Other (income) expenses, net		21
Accounting Standards Update 2016-18 [Member]
Recently Issued Accounting Standards [Line Items]
Restricted cash	7	18		$ 7	$ 6
Increase in restricted cash		12
Cash (used for) provided from investing activities		(11)
Net change in cash and cash equivalents and restricted cash		$ 1
New Accounting Pronouncement, Early Adoption, Effect [Member]
Recently Issued Accounting Standards [Line Items]
Reclassification effect	$ 350

Recently Adopted and Recently36

Recently Adopted and Recently Issued Accounting Guidance - Summary of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 1,196	$ 1,358
Restricted cash	7	7
Total	$ 1,203	$ 1,365	$ 822	$ 859

Revenue - Additional Informatio

Revenue - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Revenue from Contract with Customer [Abstract]
Number of operating segments	5

Revenue - Schedule of Product D

Revenue - Schedule of Product Division Information (Detail)	3 Months Ended
	Mar. 31, 2018
Bauxite [Member]
Product Information [Line Items]
Product Division	Bauxite
Pricing components	Negotiated
Shipping terms	FOB/CIF
Payment terms	LC Sight
Alumina [Member] | Smelter-grade [Member]
Product Information [Line Items]
Product Division	Alumina: Smelter-grade
Pricing components	API/spot
Shipping terms	FOB
Payment terms	LC Sight/CAD/Net 30 days
Alumina [Member] | Non-metallurgical [Member]
Product Information [Line Items]
Product Division	Alumina: Non-metallurgical
Pricing components	Negotiated
Shipping terms	FOB/CIF
Payment terms	Net 30 days
Primary Aluminum [Member] | Common Alloy Ingot [Member]
Product Information [Line Items]
Product Division	Primary aluminum: Common alloy ingot
Pricing components	LME + Regional premium
Shipping terms	DAP/CIF
Payment terms	Net 30 to 45 days
Primary Aluminum [Member] | Value-add Ingot [Member]
Product Information [Line Items]
Product Division	Primary aluminum: Value-add ingot
Pricing components	LME + Regional premium + Product premium
Shipping terms	DAP/CIF
Payment terms	Net 30 to 45 days
Flat-rolled Aluminum [Member]
Product Information [Line Items]
Product Division	Flat-rolled aluminum
Pricing components	Metal + Conversion
Shipping terms	DAP
Payment terms	Negotiated

Revenue - Schedule of Revenue b

Revenue - Schedule of Revenue by Product Division (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 3,090	$ 2,655
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	(17)	(11)
Primary Aluminum [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	1,647	1,352
Alumina [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	913	731
Flat-rolled Aluminum [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	429	423
Energy [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	73	90
Bauxite [Member] | Operating Segments [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 45	$ 70

Restructuring and Other Charg40

Restructuring and Other Charges - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)Employees	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Restructuring Cost and Reserve [Line Items]
Net gain related to curtailment of certain pension and other postretirement employee benefits	$ 23,000,000
Restructuring and other charges	(19,000,000)	$ 10,000,000
Cash payments	10,000,000		$ 73,000,000
Restructuring and Other Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring net benefit	19,000,000
Lease Termination [Member]
Restructuring Cost and Reserve [Line Items]
Amount of cash payments expected to be paid beyond the end of the current annual period	(3,000,000)
Contract Termination [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 4,000,000	13,000,000
Miscellaneous Charges [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2,000,000
Other Adjustments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 5,000,000
Restructuring Programs Layoffs 2017 [Member]
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | Employees	120
Number of employees associated with layoff costs | Employees	140
Cash payments	$ 2,000,000

Restructuring and Other Charg41

Restructuring and Other Charges - Schedule of Restructuring and Other Charges by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (19)	$ 10
Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	4	12
Corporate [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	(23)	(2)
Alumina [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	(1)
Aluminum Segment [Member] | Operating Segments [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 5	$ 12

Restructuring and Other Charg42

Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring reserve beginning balance	$ 45	$ 66
Cash payments	(10)	(73)
Restructuring charges	4	90
Other		(38)
Restructuring reserve ending balance	39	45
Layoff Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve beginning balance	11	38
Cash payments	(3)	(30)
Restructuring charges		23
Other		(20)
Restructuring reserve ending balance	8	11
Other Exit Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve beginning balance	34	28
Cash payments	(7)	(43)
Restructuring charges	4	67
Other		(18)
Restructuring reserve ending balance	$ 31	$ 34

Restructuring and Other Charg43

Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (19)	$ 10
Pension and Other Postretirement Benefits Costs Charged to Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Pension benefits costs			$ 8
Asset Retirement Obligations [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			10
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 8

Segment Information - Schedule

Segment Information - Schedule of Operating Results,Capital Expenditures and Assets of Alcoa's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Adjusted EBITDA	$ 655	$ 624
Depreciation, depletion, and amortization	188	168
Equity income (loss)	(1)	(6)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	3,779	3,194
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	707	584
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	3,072	2,610
Bauxite [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	110	110
Depreciation, depletion, and amortization	29	18
Bauxite [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	296	289
Bauxite [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	249	219
Bauxite [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	47	70
Alumina [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	392	297
Depreciation, depletion, and amortization	53	49
Equity income (loss)	(1)	1
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,368	1,095
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	454	361
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	914	734
Aluminum [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	153	217
Depreciation, depletion, and amortization	106	101
Equity income (loss)		(7)
Aluminum [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	2,115	1,810
Aluminum [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	4	4
Aluminum [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 2,111	$ 1,806

Segment Information - Schedul45

Segment Information - Schedule of Segment Adjusted EBITDA to Consolidated Net Income Attributable to Alcoa Corporation (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total segment Adjusted EBITDA	$ 655	$ 624
Transformation	(2)	(20)
Corporate inventory accounting	31	(17)
Corporate expenses	(27)	(33)
Provision for depreciation, depletion, and amortization	(194)	(179)
Interest expense	(26)	(26)
Other (expenses) income, net (N)	(21)	79
Income before income taxes	412	418
Provision for income taxes	(138)	(110)
Net income attributable to noncontrolling interest	(124)	(83)
Consolidated net income attributable to Alcoa Corporation	150	225
Other [Member]
Segment Reporting Information [Line Items]
Restructuring and other charges (D)	19	(10)
Interest expense	(26)	$ (26)
Other	$ (23)

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Computation of Basic and Diluted EPS Attributable to Alcoa Corporation Common Shareholders (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income attributable to Alcoa Corporation	$ 150	$ 225
Average shares outstanding - basic	186	184
Effect of dilutive securities:
Stock options	1	1
Stock and performance awards	1	1
Average shares outstanding - diluted	188	186

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) shares in Millions	3 Months Ended
	Mar. 31, 2017$ / sharesshares
CL Equity Unit Purchase Agreements [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities | shares	1
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average exercise price of options | $ / shares	$ 36.29

Accumulated Other Comprehensi48

Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension and other postretirement benefits
Total Other comprehensive income (loss)	$ 102	$ 43
Foreign currency translation
Other comprehensive income (loss)	(13)	353
Cash flow hedges
Total Other comprehensive income (loss) before reclassifications, net of tax	22
Total Other comprehensive income (loss)	530	(225)
Alcoa Corporation [Member]
Pension and other postretirement benefits
Balance at beginning of period	(2,786)	(2,330)
Unrecognized net actuarial loss and prior service cost/benefit	75	(5)
Tax (expense) benefit	(8)	1
Total Other comprehensive income (loss) before reclassifications, net of tax	67	(4)
Amortization of net actuarial loss and prior service cost/benefit	36	50
Tax benefit (expense)	(2)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	34	48
Total Other comprehensive income (loss)	101	44
Balance at end of period	(2,685)	(2,286)
Foreign currency translation
Balance at beginning of period	(1,467)	(1,655)
Other comprehensive income (loss)	1	239
Balance at end of period	(1,466)	(1,416)
Cash flow hedges
Balance at beginning of period	(929)	210
Net change from periodic revaluations	635	(380)
Tax (expense) benefit	(99)	58
Total Other comprehensive income (loss) before reclassifications, net of tax	536	(322)
Net amount reclassified to earnings	13	17
Tax benefit (expense)	1	(3)
Total amount reclassified from Accumulated other comprehensive income (loss), net of tax	14	14
Total Other comprehensive income (loss)	550	(308)
Balance at end of period	(379)	(98)
Alcoa Corporation [Member] | Aluminum Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	27	18
Alcoa Corporation [Member] | Financial Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	(13)	(1)
Alcoa Corporation [Member] | Foreign Exchange Contract [Member]
Cash flow hedges
Net amount reclassified to earnings	(1)
Non-controlling Interest [Member]
Pension and other postretirement benefits
Balance at beginning of period	(47)	(56)
Unrecognized net actuarial loss and prior service cost/benefit	1	(1)
Tax (expense) benefit	(1)
Total Other comprehensive income (loss) before reclassifications, net of tax		(1)
Amortization of net actuarial loss and prior service cost/benefit	1
Total amount reclassified from Accumulated other comprehensive loss, net of tax	1
Total Other comprehensive income (loss)	1	(1)
Balance at end of period	(46)	(57)
Foreign currency translation
Balance at beginning of period	(581)	(677)
Other comprehensive income (loss)	(14)	114
Balance at end of period	(595)	(563)
Cash flow hedges
Balance at beginning of period	51	1
Net change from periodic revaluations	(20)	120
Tax (expense) benefit	6	(36)
Total Other comprehensive income (loss) before reclassifications, net of tax	(14)	84
Net amount reclassified to earnings	(9)	(1)
Tax benefit (expense)	3
Total amount reclassified from Accumulated other comprehensive income (loss), net of tax	(6)	(1)
Total Other comprehensive income (loss)	(20)	83
Balance at end of period	31	84
Non-controlling Interest [Member] | Financial Contracts [Member]
Cash flow hedges
Net amount reclassified to earnings	$ (9)	$ (1)

Investments - Summary of Unaudi

Investments - Summary of Unaudited Financial Information for Alcoa Corporation's Equity Investments (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments Schedule [Abstract]
Sales	$ 1,253	$ 916
Cost of goods sold	960	678
Net income	$ 65	$ 23

Inventories - Schedule of Inven

Inventories - Schedule of Inventory Components (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods	$ 347	$ 296
Work-in-process	314	258
Bauxite and alumina	581	585
Purchased raw materials	551	473
Operating supplies	145	147
LIFO reserve	(308)	(306)
Inventories, total	$ 1,630	$ 1,453

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories valued on a LIFO basis	$ 561	$ 516
Inventories valued on a LIFO basis percentage	29.00%	29.00%

Pension and Other Postretirem52

Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Curtailments	$ (23)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	$ 18
Interest cost	59	61
Expected return on plan assets	(90)	(99)
Recognized net actuarial loss	55	46
Amortization of prior service benefit	2	2
Curtailments	5
Net periodic benefit cost	45	28
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	9	9
Recognized net actuarial loss	3	3
Amortization of prior service benefit		(1)
Curtailments	(28)
Net periodic benefit cost	$ (15)	$ 12

Pension and Other Postretirem53

Pension and Other Postretirement Benefits - Additional Information (Detail) $ in Millions	Jan. 17, 2018	Mar. 31, 2018USD ($)Employee	Jan. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Number of employees affected the change in defined contribution plans	800
Percentage of employers contribution in defined benefit plans	3.00%
Curtailment gain (charge) on net pension and other postretirement benefits		$ 23
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of employees covered under defined benefit plans | Employee		54,000
Discount rate used to determine pension benefit obligation			3.80%	3.65%
Increase (decrease) of benefit plan obligations for plan amendment		$ (57)
Curtailment gain (charge) on net pension and other postretirement benefits		$ (5)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of employees covered under defined benefit plans | Employee		48,000
Number of employees affected the change in defined contribution plans | Employee		700
Discount rate used to determine pension benefit obligation			3.43%	3.29%
Increase (decrease) of benefit plan obligations for plan amendment		$ (7)
Curtailment gain (charge) on net pension and other postretirement benefits		$ 28

Derivatives and Other Financi54

Derivatives and Other Financial Instruments - Additional Information (Detail) kT in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018USD ($)MWhDerivativeSmelterRefinerykT	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)MWhkT	Dec. 31, 2016USD ($)MWh
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of derivative contracts recorded as assets	$ 124,000,000		$ 197,000,000
Fair value of derivative contracts recorded as liabilities	$ 531,000,000		1,173,000,000
Other derivative contracts estimated term of quoted market prices, in years	10 years
Recognized an unrealized gain (loss)	$ 22,000,000
Electricity purchases	In addition, in January 2017, Alcoa Corporation entered into a new financial contract that hedges the anticipated power requirements at this smelter for the period from August 2017 through July 2021 (see D11 above). At March 31, 2018 and December 31, 2017, this financial contract hedges forecasted electricity purchases of 8,199,576 and 8,805,456, respectively, megawatt hours.
Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of derivative contracts recorded as assets	$ 27,000,000		44,000,000
Fair value of derivative contracts recorded as liabilities	48,000,000		117,000,000
Other Expenses (Income) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) recognized	4,000,000
Cash Flow Hedging [Member] | Other Comprehensive Loss [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) recognized	$ 68,000,000		50,000,000
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of smelters | Smelter	9
Number of refineries | Refinery	3
London Metal Exchange [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative	2
LME Plus Midwest Premium [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative	3
Derivatives Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of derivative contracts recorded as assets	$ 124,000,000		197,000,000
Fair value of derivative contracts recorded as liabilities	$ 490,000,000		1,112,000,000
Number of derivative instruments | Derivative	1
Derivatives Not Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of derivative contracts recorded as liabilities	$ 41,000,000		61,000,000
Number of derivative instruments | Derivative	1
Derivatives Not Designated as Hedging Instruments [Member] | Other Expenses (Income), Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments	$ 17,000,000	$ 25,000,000
Energy Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Increase (decrease) in derivative asset				$ (84,000,000)
Energy Contracts [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) recognized				(6,000,000)
Other income				$ 7,000,000
Energy Contracts [Member] | Derivative D11 [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) recognized	(46,000,000)		$ (22,000,000)
Energy Contracts [Member] | Other Comprehensive Loss [Member] | Derivative D11 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) recognized	(51,000,000)	169,000,000
Energy Contracts [Member] | Other Expenses (Income) [Member] | Derivative D11 [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss)	$ 1,000,000
Energy Contracts [Member] | Derivatives Designated as Hedging Instruments [Member] | Derivative D11 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forecasted energy purchases in megawatt hours | MWh	8,199,576		8,805,456	1,969,544
Energy Contracts [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments		34,000,000
Embedded Aluminum Derivative [Member] | Cash Flow Hedging [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognized an unrealized gain (loss)	$ 597,000,000	(498,000,000)
Realized gain (loss) on derivatives	$ (25,000,000)	(18,000,000)
Embedded Aluminum Derivative [Member] | Derivatives Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aluminum forecast sales | kT	2,743		2,859
Embedded Aluminum Derivative [Member] | Derivatives Designated as Hedging Instruments [Member] | Cash Flow Hedging [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of gain (loss) expected to be recognized into earnings over the next 12 months		(67,000,000)
Derivative instruments ineffectiveness	$ 0	0
Embedded Aluminum Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments	$ 6,000,000	(14,000,000)
Embedded Aluminum Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of derivative instruments | Derivative	2
Embedded Credit Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract period	10 years
Derivative contract period, description	As Alcoa Corporation does not have outstanding 30-year debt, the Company’s estimated 30-year debt yield is represented by the sum of (i) the excess of the yield on Alcoa’s outstanding notes due 2026 over the yield on only the Ba/BB-rated company debt included in Barclays High Yield Index for intermediate (10-year) credits and (ii) the yield on only the Ba/BB-rated company debt included in Barclays High Yield Index for long (30-year) credits. In accordance with the terms of the power contract, this calculation may be changed in January of each calendar year.
Embedded Credit Derivative [Member] | Negotiated multiplier [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract period	30 years
Embedded Credit Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net gain (loss) of derivative instruments	$ 11,000,000	$ 5,000,000

Derivatives and Other Financi55

Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)MWh$ / Metric_Ton$ / lb$ / MWh$ / Barrels	Dec. 31, 2017USD ($)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value | $	$ 124	$ 197
Derivative D7 [Member] | Energy Contracts [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Level 3 [Member] | Average Price [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,991
Maturity month and year of future aluminum price	2018-04
Expected future oil prices | $ / Barrels	70
Maturity month and year of future oil price	2018-01
Derivative D7 [Member] | Energy Contracts [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Level 3 [Member] | Average Price [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,019
Maturity month and year of future aluminum price	2018-10
Expected future oil prices | $ / MWh	67
Maturity month and year of future oil price	2018-10
Derivative D11 [Member] | Energy Contracts [Member] | Interrelationship of Forward Energy Price and the Consumer Price Index and Price of Electricity Beyond Forward Curve [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Assets, Fair value | $	$ 124
Derivative D11 [Member] | Energy Contracts [Member] | Interrelationship of Forward Energy Price and the Consumer Price Index and Price of Electricity Beyond Forward Curve [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve | $ / MWh	65.43
Maturity date of electricity beyond forward curve	2,018
Derivative D11 [Member] | Energy Contracts [Member] | Interrelationship of Forward Energy Price and the Consumer Price Index and Price of Electricity Beyond Forward Curve [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Price of electricity beyond forward curve | $ / MWh	53.88
Maturity date of electricity beyond forward curve	2,021
Derivative D1 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum One [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 281
Megawatt hours per year | MWh	4,000,000
Derivative D1 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum One [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,991
Maturity year of future aluminum price	2,018
Derivative D1 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum One [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,368
Maturity year of future aluminum price	2,027
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 198
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Average Price [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,408
Maturity year of future aluminum price	2,028
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Midwest Premium [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium | $ / lb	0.1900
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Midwest Premium [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium | $ / lb	0.1900
Midwest Premium expected year	2,018
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Two Contracts [Member] | Level 3 [Member] | Average Price [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,476
Maturity year of future aluminum price	2,029
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Two Contracts [Member] | Level 3 [Member] | Midwest Premium [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium expected year	2,029
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | One Contract [Member] | Level 3 [Member] | Average Price [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,771
Maturity year of future aluminum price	2,036
Derivative D3 Through D5 [Member] | Energy Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | One Contract [Member] | Level 3 [Member] | Midwest Premium [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Midwest Premium expected year	2,036
Derivative D8 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 25
Midwest Premium | $ / lb	0.1900
Price of electricity beyond forward curve | $ / MWh	2,000,000
Derivative D8 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Level 3 [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	1,991
Maturity year of future aluminum price	2,018
Midwest Premium expected year	2,018
Derivative D8 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Amount of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Level 3 [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,037
Maturity year of future aluminum price	2,019
Midwest Premium expected year	2,019
Derivative D2 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 11
Derivative D2 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member] | Average Price [Member] | Minimum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,110
Maturity year of future aluminum price	2,019
Derivative D2 [Member] | Energy Contracts [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member] | Average Price [Member] | Maximum [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Expected future aluminum prices	2,061
Maturity year of future aluminum price	2,019
Derivative D9 [Member] | Energy Contracts [Member] | Estimated Difference In Credit Spread Of Each Of Alcoa Corporation And Counterparty, And Negotiated Multiplier [Member] | Level 3 [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Liabilities, Fair value | $	$ 16
Percentage of credit spread	2.05%
Derivative D9 [Member] | Energy Contracts [Member] | Estimated Difference In Credit Spread Of Each Of Alcoa Corporation And Counterparty, And Negotiated Multiplier [Member] | Level 3 [Member] | Counterparty [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	4.12%
Derivative D9 [Member] | Energy Contracts [Member] | Estimated Difference In Credit Spread Of Each Of Alcoa Corporation And Counterparty, And Negotiated Multiplier [Member] | Level 3 [Member] | Alcoa Corporation [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of credit spread	6.17%

Derivatives and Other Financi56

Derivatives and Other Financial Instruments - Schedule of Fair Values of Level 3 Derivative Instruments Recorded as Assets and Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	$ 124	$ 197
Fair value liability derivatives	531	1,173
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	124	197
Fair value liability derivatives	490	1,112
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Financial Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	46	96
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Financial Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	78	101
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Embedded Aluminum Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	67	120
Derivatives Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Embedded Aluminum Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	423	992
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	41	61
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Embedded Aluminum Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	25	28
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Current [Member] | Embedded Credit Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	3	4
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Embedded Aluminum Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives		6
Derivatives Not Designated as Hedging Instruments [Member] | Fair Value of Derivative Contracts - Noncurrent [Member] | Embedded Credit Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value liability derivatives	$ 13	$ 23

Derivatives and Other Financi57

Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Embedded Aluminum Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	$ 1,146
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other comprehensive income	(597)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements	0
Fair value measurement, Liabilities,Transfers into and/or out of Level 3	0
Fair value measurement, Liabilities, Other	(3)
Fair value measurement, Liabilities, Ending balance	515
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other income, net	(6)
Embedded Aluminum Derivative [Member] | Sales [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(25)
Embedded Aluminum Derivative [Member] | Other Expense [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(6)
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	27
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements	0
Fair value measurement, Liabilities,Transfers into and/or out of Level 3	0
Fair value measurement, Liabilities, Ending balance	16
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other income, net	(11)
Embedded Credit Derivative [Member] | Other Expense [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(11)
Financial Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	197
Fair value measurement, Assets, Other comprehensive income	(51)
Fair value measurement, Assets, Purchases, sales, issuances, and settlements	0
Fair value measurement, Assets, Transfers into and/or out of Level 3	0
Fair value measurement, Assets, Other	0
Fair value measurement, Assets, Ending balance	124
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	0
Financial Contracts [Member] | Cost of Goods Sold [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets	(22)
Fair value measurement, Assets	$ (22)

Derivatives and Other Financi58

Derivatives and Other Financial Instruments - Schedule of Carrying Values and Fair Values of Other Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Carrying Value [Member]
Derivative [Line Items]
Cash and cash equivalents	$ 1,196	$ 1,358
Restricted cash	7	7
Long-term debt due within one year	15	16
Long-term debt, less amount due within one year	1,445	1,388
Fair Value [Member]
Derivative [Line Items]
Cash and cash equivalents	1,196	1,358
Restricted cash	7	7
Long-term debt due within one year	15	16
Long-term debt, less amount due within one year	$ 1,574	$ 1,555

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Corporate income tax rate	21.00%	35.00%
Discrete income tax charge related to TCJA		$ 22
Minimum [Member]
Income Taxes [Line Items]
Percentage of deductible expenses	3.00%

Contingencies and Commitments -

Contingencies and Commitments - Additional Information (Detail) € in Millions, $ in Millions	Jan. 31, 2018USD ($)	Jan. 31, 2018EUR (€)	Dec. 31, 2015USD ($)	Dec. 31, 2015EUR (€)	Mar. 31, 2018USD ($)	Mar. 31, 2018EUR (€)
Commitments and Contingencies Disclosure [Abstract]
Management estimate for maximum exposure from class action					$ 97	€ 76
Partial Reserve			$ 37	€ 34
Litigation settlement	$ 18	€ 15
Reduction in restructuring and other charges reserve	$ 22	€ 19

Contingencies and Commitments61

Contingencies and Commitments - Additional Information - 1 (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Remediation reserve balance	$ 284	$ 294
Remediation reserve balance, classified as a current liability	50	36
Payments related to remediation expenses applied against the reserve	6
Increase (Decrease) in reserves due to effects of foreign currency translation	1
Reclassification of amounts included in asset retirement obligations	(5)
Sherwin, TX Site [Member]
Loss Contingencies [Line Items]
Remediation reserve balance	$ 29	$ 29

Contingencies and Commitments62

Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, ر.س in Billions	Apr. 08, 2013BRL (R$)	Apr. 08, 2013USD ($)	Mar. 31, 2013BRL (R$)	May 31, 2012BRL (R$)	May 31, 2012USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2018SAR (ر.س)	Dec. 31, 2017USD ($)	Mar. 31, 2018EUR (€)	Apr. 08, 2013USD ($)	Mar. 31, 2013USD ($)
Loss Contingencies [Line Items]
Remediation reserve balance						$ 284,000,000		$ 294,000,000
Alumina Limited [Member]
Loss Contingencies [Line Items]
Percentage of amount required to be contributed in the event Alcoa would be required to make payments under the guarantees						40.00%	40.00%
Other Noncurrent Liabilities and Deferred Credits [Member]
Loss Contingencies [Line Items]
Guarantee issued on behalf of smelting and rolling mill companies						$ 3,000,000		3,000,000
Financial Guarantee [Member]
Loss Contingencies [Line Items]
Debt service requirements, principal						122,000,000
Debt service requirements, interest maximum						35,000,000
AWAC [Member]
Loss Contingencies [Line Items]
Project financing Investment						830,000,000
Tax Year 2006 Through 2009 [Member] | Tax Authority, Spain [Member]
Loss Contingencies [Line Items]
Total combined assessments						161,000,000			€ 130
Alcoa World Alumina Brasil [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Disallowed tax credits			R$ 220000000								$ 110,000,000
Percentage of penalty of the gross disallowed amount	50.00%	50.00%	50.00%
Value added tax receivable				R$ 82000000	$ 41,000,000
Alcoa World Alumina Brasil [Member] | Minimum [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Estimated range of reasonably possible loss, minimum		$ 0
Alcoa World Alumina Brasil [Member] | Minimum [Member] | Fixed Assets [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Disallowed tax credits										$ 0
Alcoa World Alumina Brasil [Member] | Maximum [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Estimated range of reasonably possible loss, minimum	R$ 103000000	$ 31,000,000
Alcoa World Alumina Brasil [Member] | Maximum [Member] | Fixed Assets [Member] | Brazilian Federal Revenue Office [Member]
Loss Contingencies [Line Items]
Disallowed tax credits	R$ 117000000									$ 35,000,000
Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Contribution to joint venture								66,000,000
Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Project financing Investment						3,308,000,000
Baie Comeau [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						4,000,000		5,000,000
Payments related to remediation expenses applied against the reserve								(4,000,000)
Fusina [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						8,000,000		8,000,000
Portovesme [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						15,000,000		16,000,000
Mosjoen [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						2,000,000		1,000,000
Increase (decrease) in remediation reserve								(2,000,000)
East St. Louis, IL Site [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						$ 4,000,000
Long-term inspection, maintenance, and monitoring program period in years						30 years	30 years
Sherwin [Member]
Loss Contingencies [Line Items]
Remediation reserve balance						$ 29,000,000
Ma'aden Joint Venture [Member] | Saudi Arabia [Member]
Loss Contingencies [Line Items]
Ownership interest in joint venture						74.90%	74.90%
Contribution to joint venture								199,000,000
Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Ownership interest in joint venture						25.10%	25.10%
Maaden Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Equity investments						$ 885,000,000		$ 887,000,000
Maaden Alcoa Joint Venture [Member] | Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Expected project investment						1,100,000,000
Capital investment commitment paid-to-date						982,000,000
Maaden Alcoa Joint Venture [Member] | Saudi Arabia [Member]
Loss Contingencies [Line Items]
Expected project investment						$ 10,800,000,000	ر.س 40.5

Other Expenses (Income), Net -

Other Expenses (Income), Net - Schedule of Other Expenses (Income), Net (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Income and Expenses [Abstract]
Equity loss	$ 2	$ 7
Foreign currency losses, net	3	16
Net gain from asset sales	(5)	(120)
Net gain on mark-to-market derivative instruments	(17)	(3)
Non-service costs - Pension & OPEB	38	21
Other (income) expenses, net	$ 21	$ (79)

Other Expenses (Income), Net 64

Other Expenses (Income), Net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other Non operating Income Expense [Line Items]
Net gain from asset sales	$ 5	$ 120
United States [Member]
Other Non operating Income Expense [Line Items]
Net gain from asset sales		$ 120

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Millions	Apr. 03, 2018USD ($)Employee$ / shares	Jan. 17, 2018
Subsequent Event [Line Items]
Retirement plan, number of participants		800
Subsequent Event [Member]
Subsequent Event [Line Items]
Number of retirees covered under annuity contract	2,100
Benefit obligation of retirement plans	$ 555
Defined benefit pension plans, transaction fee	25
Company's contribution	$ 95
Retirement plan, number of participants | Employee	3,500
Non-cash settlement charge	$ 175
Non-cash settlement charge, net of tax	$ 128
Non-cash settlement charge, net of tax, per share | $ / shares	$ 0.68