XML 65 R52.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Pension and Other Postretirement Benefits - Narrative (Detail) |  |  | 1 Months Ended | 3 Months Ended
--- | --- | --- | --- | ---
Apr. 01, 2018 USD ($) | Nov. 01, 2016 USD ($) Installments | Mar. 31, 2018 USD ($) | Apr. 30, 2017 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits |  |  |  |  | $ 143,000,000 | $ 31,000,000
Cash contribution term to pension plan |  | 30 months |  |  |  |
Number of installments | Installments |  | 3 |  |  |  |
Minimum required cash contribution to pension plan |  | $ 50,000,000 |  |  |  |
Aggregate cash cash contribution to pension plan |  | $ 150,000,000 |  |  |  |
Cash payments made for pension and other post-retirement benefits |  |  | $ 50,000,000 | $ 50,000,000 |  |
Pension Benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Curtailments |  |  |  |  | $ 5,000,000 | $ 0
UNITED STATES | Pension Benefits |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Increase (decrease) in obligation, pension benefits | $ 136,000,000 |  |  |  |  |
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits | 141,000,000 |  |  |  |  |
Curtailments | $ 5,000,000 |  |  |  |  |

X
- Definition Aggregate cash contribution to pension plan. + References No definition available. + Details
Name: | arnc_AggregateCashContributionToPensionPlan
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Cash contribution term to pension plan. + References No definition available. + Details
Name: | arnc_CashContributionTermToPensionPlan
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Minimum required cash contribution to pension plan. + References No definition available. + Details
Name: | arnc_MinimumRequiredCashContributionToPensionPlan
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of installment made for cash contribution to pension plan. + References No definition available. + Details
Name: | arnc_NumberOfInstallmentMadeForCashContributionToPensionPlan
Namespace Prefix: | arnc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(7) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase (decrease) in obligation for pension benefits. Includes, but is not limited to, defined benefit or defined contribution plans. Excludes other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInPensionPlanObligations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669646-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of payment for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585 + Details
Name: | us-gaap_PensionAndOtherPostretirementBenefitContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |