Accrual For Environmental Loss Contingencies, Increase (Decrease) For Other Items

No definition available.

Name:	arnc_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForOtherItems
Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Income (Loss) Before Interest, Taxes, Depreciation and Amortization, Adjusted

+ References

No definition available.

+ Details

Name:	arnc_IncomeLossBeforeInterestTaxesDepreciationAndAmortizationAdjusted
Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Loss Contingency, Number Of Additional Plaintiffs

+ References

No definition available.

+ Details

Name:	arnc_LossContingencyNumberOfAdditionalPlaintiffs
Namespace Prefix:	arnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loss, Contingency, Number Of Plaintiffs Withdrawn

+ References

No definition available.

+ Details

Name:	arnc_LossContingencyNumberOfPlaintiffsWithdrawn
Namespace Prefix:	arnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loss Contingency, Number Of Subsidiaries

+ References

No definition available.

+ Details

Name:	arnc_LossContingencyNumberOfSubsidiaries
Namespace Prefix:	arnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loss Contingency, Number of Former Executives

+ References

No definition available.

+ Details

Name:	arnc_LossContingencyNumberofFormerExecutives
Namespace Prefix:	arnc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Of Cash

+ References

No definition available.

+ Details

Name:	arnc_PercentageOfCash
Namespace Prefix:	arnc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage Of Liquidity

+ References

No definition available.

+ Details

Name:	arnc_PercentageOfLiquidity
Namespace Prefix:	arnc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage Of Segment Adjusted EBITDA

+ References

No definition available.

+ Details

Name:	arnc_PercentageOfSegmentAdjustedEBITDA
Namespace Prefix:	arnc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Of Third Party Sales

+ References

No definition available.

+ Details

Name:	arnc_PercentageOfThirdPartySales
Namespace Prefix:	arnc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value as of the balance sheet date of obligations incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References

+ Details

Name:	us-gaap_AccountsPayableTradeCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total costs accrued as of the balance sheet date for environmental loss contingencies.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of expense for newly incurred environmental loss contingencies. Includes, but is not limited to, remediation expense and interest accretion.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q2)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesChargesToExpenseForNewLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) in the obligation for environmental loss contingencies from business acquisitions (divestitures).

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForAcquisitionsAndDivestitures
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of expense (reversal of expense) which increases (decreases) the accrual for environmental loss contingencies from revisions in estimates to existing obligations. Excludes changes related to business acquisitions, divestitures, or currency movement.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash outflow to settle environmental loss contingencies.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 5.Y.Q1)
-URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3367-108585

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesPayments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increase (decrease) in the accrual for environmental loss contingencies during the reporting period.

+ References

+ Details

Name:	us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 10
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=124098289&loc=d3e6911-107765

+ Details

Name:	us-gaap_AccruedEnvironmentalLossContingenciesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3044-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3521-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3044-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=123431023&loc=SL98516268-108586

+ Details

Name:	us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

Name:	us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of loss contingency liability.

+ References

+ Details

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

+ Details

Name:	us-gaap_LossContingencyDamagesSoughtValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The total number of new claims filed pertaining to a loss contingency during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349

+ Details

Name:	us-gaap_LossContingencyNewClaimsFiledNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of defendants named in a legal action.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfDefendants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plaintiffs that have filed claims pertaining to a loss contingency.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingencyNumberOfPlaintiffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SiteContingencyLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFifthAnniversary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFourthAnniversary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnSecondAnniversary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnThirdAnniversary
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of fixed and determinable portion of unrecorded unconditional purchase obligation to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationDueAfterFiveYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_StatementGeographicalAxis=country_RU
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=arnc_SamaraRussiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=arnc_ABLCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=arnc_HowmetAerospaceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=arnc_ArconicCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=arnc_AlcoaCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_SuretyBondMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_DamageFromFireExplosionOrOtherHazardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByBirnbergPeirceLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByHoweCoSolicitorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByRussellCookeLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByDeightonPierceGlynnMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedBySMQLegalServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByScottMoncrieffMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedBySaundersLawMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByImranKhanAndPartnersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByHoweAndCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByHodgeJonesAndAllenSolicitorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByHickmanAndRoseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByDuncanLewisSolicitorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByBindmansLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedByBhattMurphyLtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireEmergencyRespondersRepresentedByThompsonsSolicitorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireEmergencyRespondersRepresentedByPenningtonsManchesCooperLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireEmergencyRespondersRepresentedByPattinsonAndBrewerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_Behrensv.ArconicMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_Sullivanv.ArconicInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_AirbusMattersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_DamagesFromProductDefectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_GrenfellTowerFireSurvivorsAndEstatesOfDecedentsRepresentedBySlaterGordonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=arnc_FederalAntimonopolyServicesOfTheRussianFederationLitigationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_UnfavorableRegulatoryActionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=arnc_AluminumRollingMillinItapissumaBrazilMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=arnc_ActiveRemediationSystemsAndMonitoringAndInspectionProgramsAtSeveralSitesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationSiteAxis=arnc_MassenaWestNYMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=us-gaap_ConstructionInProgressMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnvironmentalRemediationContingencyAxis=us-gaap_MaintenanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=arnc_LegalMattersOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Contingencies and Commitments (Details) $ in Millions							1 Months Ended	8 Months Ended		12 Months Ended
Contingencies and Commitments (Details) $ in Millions	Dec. 23, 2020 claimant defendant	Jun. 26, 2020 claimant	Jun. 12, 2020 USD ($) firefighter claimant police_officer	Jun. 11, 2020 firefighter	Jun. 06, 2019 plaintiff	Sep. 15, 2017 executive	Jun. 30, 2019 USD ($)	Feb. 23, 2021 firefighter	Feb. 23, 2021 firefighter	Dec. 31, 2021 USD ($) claimant segment firefighter police_officer	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) request
Site Contingency [Line Items]
Environmental remediation										$ 64.0	$ 156.0
Environmental remediation, current										15.0	90.0
Accounts payable, trade										1,718.0	1,106.0
Remediation reserve decrease										(5.0)	2.0
Remediation reserve reversal liability											5.0
Environmental remediation, additions										5.0
Environmental remediation, payments										84.0	82.0	$ 56.0
Environmental remediation, increase for obligations transferred in connection with Separation										13.0
Environmental remediation, decrease for other items										3.0
Purchase commitments due in 2021										3,287.0
Purchase commitments due in 2022										270.0
Purchase commitments due in 2023										40.0
Purchase commitments due in 2024										37.0
Purchase commitments due in 2025										35.0
Purchase commitments due thereafter										24.0
Guarantor obligations, carrying value										2.0
Total amount committed under letters of credit										10.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents										335.0	787.0	72.0	$ 81.0
Cash and cash equivalents										335.0	787.0
Total sales										7,504.0	5,675.0	7,277.0
Russia
Site Contingency [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents										$ 79.0
Percentage Of Cash										24.00%
Percentage of Liquidity										7.00%
Total sales										$ 793.0	535.0	512.0
Samara, Russia
Site Contingency [Line Items]
Total sales										$ 968.0
Percentage Of Third Party Sales										16.00%
Segment Adjusted EBITDA										$ 87.0
Percentage Of Segment Adjusted EBITDA										13.00%
Revolving Credit Facility \| ABL Credit Agreement \| Credit Facility
Site Contingency [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount										$ 790.0
Howmet Aerospace \| Arconic Corporation
Site Contingency [Line Items]
Guarantor obligations, carrying value										0.0
Total amount committed under letters of credit										27.0
Alcoa Corporation \| Arconic Corporation
Site Contingency [Line Items]
Guarantor obligations, carrying value										16.0
Total amount committed under letters of credit										0.0
Surety Bonds
Site Contingency [Line Items]
Total amount committed under surety bonds										43.0
Surety Bonds \| Howmet Aerospace \| Arconic Corporation
Site Contingency [Line Items]
Total amount committed under surety bonds										4.0
Surety Bonds \| Alcoa Corporation \| Arconic Corporation
Site Contingency [Line Items]
Total amount committed under surety bonds										$ 5.0
Grenfell Tower Fire, Survivors and Estates of Decedents \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of defendants \| defendant	23
Survivors and Estates of Decedents, Represented by Birnberg Peirce Ltd \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	118		4							113
Survivors and Estates of Decedents, Represented by Howe & Co Solicitors \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant			2
Survivors and Estates of Decedents, Represented by Russell-Cooke LLP \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	34	3								33
Survivors and Estates of Decedents, Represented by Deighton Pierce Glynn \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	7
GreSurvivors and Estates of Decedents, Represented by SMQ Legal Services \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	5									6
Survivors and Estates of Decedents, Represented by Scott Moncrieff \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	4									3
Survivors and Estates of Decedents, Represented by Saunders Law \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	31									27
Survivors and Estates of Decedents, Represented by Imran Khan & Partners \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	40									47
Survivors and Estates of Decedents, Represented by Howe & Co \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	61									58
Survivors and Estates of Decedents, Represented by Hodge Jones and Allen Solicitor \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	114
Survivors and Estates of Decedents, Represented by Hickman & Rose \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	19									23
Survivors and Estates of Decedents, Represented by Duncan Lewis Solicitors \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	5									10
Survivors and Estates of Decedents, Represented by Bindmans LLP \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	341
Survivors and Estates of Decedents, Represented by Bhatt Murphy Ltd \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	82									76
Emergency Responders, Represented by Thompsons Solicitors \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| firefighter				98						80
Number of additional plaintiffs added to suit \| firefighter									10	7
Emergency Responders, Represented by Penningtons Manches Cooper LLP \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| police_officer			27							36
Emergency Responders, Represented by Pattinson and Brewer \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| firefighter			2
Number of claimants withdrawn from suit \| firefighter								1
Behrens v. Arconic
Site Contingency [Line Items]
Number of claimants/plaintiffs \| plaintiff					247
Sullivan v. Arconic
Site Contingency [Line Items]
Number of former executives \| executive						3
Airbus Matters \| Damages from Product Defects
Site Contingency [Line Items]
Number of separate confidential requests for arbitration \| request													3
Damages sought (in excess of)			$ 200.0
Grenfell Tower Fire, Survivors And Estates Of Decedents, Represented By Slater & Gordon \| Grenfell Tower Fire
Site Contingency [Line Items]
Number of claimants/plaintiffs \| claimant	27									24
Federal Antimonopoly Services of the Russian Federation Litigation \| Non-Compliance with Russian Federal Law No. 57-FZ
Site Contingency [Line Items]
Loss Contingency, Number Of Subsidiaries \| segment										2
Aluminum Rolling Mill in Brazil
Site Contingency [Line Items]
Environmental remediation, additions											1.0
Active Remediation Systems and/or Monitoring and Inspection Programs at Several Sites
Site Contingency [Line Items]
Environmental remediation, additions											2.0
Environmental remediation, decrease for other items										$ 4.0
Massena West, NY
Site Contingency [Line Items]
Environmental remediation										30.0	$ 115.0
Remediation reserve reversal liability										(11.0)		$ 25.0
Environmental remediation, additions							$ 25.0
Massena West, NY \| Construction work-in-progress
Site Contingency [Line Items]
Environmental remediation										5.0
Massena West, NY \| Maintenance
Site Contingency [Line Items]
Environmental remediation										25.0
Massena West, NY \| Legal Matters, Other
Site Contingency [Line Items]
Remediation reserve reversal liability										$ (2.0)