XML 148 R115.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($) |  |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Apr. 01, 2018 | Apr. 18, 2017 | Aug. 01, 2016 | Sep. 30, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Average duration refined yield curve model parallels the plans, years |  |  |  |  |  | 11 years |  |
Rate of compensation increase |  |  |  |  |  | 3.50% | 3.50% | 3.50%
Average period of historical returns used to calculate expected future returns, in years |  |  |  |  |  | 5 years |  |
Decrease in expected long-term rate of return |  |  |  |  |  | 0.75% |  | 0.25%
Pension and other postretirement plans, expected long-term rate of return, average of actual results, period of measurement |  |  |  |  |  | 20 years |  |
Expected long term rate of return on plan assets |  |  |  |  |  | 7.75% | 7.75% | 7.75%
Health care cost trend rate assumed for next year |  |  |  |  |  | 5.50% | 5.50% | 5.50%
Number of years over actual annual health care cost trend experience |  |  |  |  |  | 3 years |  |
Health care cost trend rate |  |  |  |  |  | 4.50% | 4.50% | 4.50%
Cash contribution to pension plans |  |  |  |  |  | $ 310,000,000 | $ 290,000,000 | $ 470,000,000
Minimum required cash contribution to pension plan |  |  |  | $ 50,000,000 |  | 350,000,000 |  |
Aggregate cash cash contribution to pension plan |  |  |  | $ 150,000,000 |  |  |  |
Cash contribution term to pension plan |  |  |  | 30 months |  |  |  |
Employer contributions |  | $ 50,000,000 |  |  |  |  |  |
Expenses related to saving and investment plans |  |  |  |  |  | $ 89,000,000 | 71,000,000 | 83,000,000
Maximum |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Health care cost trend rate |  |  |  |  |  | 9.00% |  |
Minimum |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Health care cost trend rate |  |  |  |  |  | 2.20% |  |
Scenario, Forecast |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Expected long term rate of return on plan assets |  |  |  |  | 7.00% |  |  |
Pension benefits |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment |  |  |  |  |  | $ 0 | 0 | (9,000,000)
Rate of compensation increase |  |  |  |  |  | 3.50% |  |
Average period over which rate of compensation increases, years |  |  |  |  |  | 5 years |  |
Change in interest cost component of net periodic benefit cost determination |  |  |  |  |  | $ 34,000,000 | 84,000,000 |
Employer contributions |  |  |  |  |  | 310,000,000 | 296,000,000 |
Other postretirement benefits |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment |  |  |  |  |  | 0 | 0 | $ 4,000,000
Change in interest cost component of net periodic benefit cost determination |  |  |  |  |  | 6,000,000 | 14,000,000 |
Employer contributions |  |  |  |  |  | 0 | $ 0 |
United Steelworkers Labor Agreement |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Increase in pension liability, plan amendment |  |  | $ 845,000,000 |  |  |  |  |
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment |  |  | $ (551,000,000) |  |  |  |  |
United States |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Minimum required cash contribution to pension plan |  |  |  |  |  | $ 320,000,000 |  |
Subsequent Event | Salaried And Retirement Savings Plan |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Retirement savings plan, employer contribution, percent | 3.00% |  |  |  |  |  |  |
Retirement savings plan, additional employer contribution, percent | 3.00% |  |  |  |  |  |  |

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 Average duration refined yield curve model parallels the plans. + References No definition available. + Details
Name: | arnc_AverageDurationRefinedYieldCurveModelParallelsPlans
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Average period of historical returns used to calculate expected future returns, years. + References No definition available. + Details
Name: | arnc_AveragePeriodOfHistoricalReturnsUsedToCalculateExpectedFutureReturns
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Basis point of decrease identified in long term rate of return. + References No definition available. + Details
Name: | arnc_BasisPointOfDecreaseIdentifiedInLongTermRateOfReturn
Namespace Prefix: | arnc_
Data Type: | num:percentItemType
Balance Type: | na
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 Defined Benefit Plan, Additional Employer Contribution, Percent + References No definition available. + Details
Name: | arnc_DefinedBenefitPlanAdditionalEmployerContributionPercent
Namespace Prefix: | arnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Benefit Plan, Employer Contribution, Percent + References No definition available. + Details
Name: | arnc_DefinedBenefitPlanEmployerContributionPercent
Namespace Prefix: | arnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The estimated reduction in interest cost upon application of change in accounting estimate in next fiscal year. + References No definition available. + Details
Name: | arnc_DefinedBenefitPlanInterestCostChangeInAccountingEstimateImpact
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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 No of year over actual annual health care cost trend experience. + References No definition available. + Details
Name: | arnc_NoOfYearOverActualAnnualHealthcareCostTrendExperience
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Pension And Other Postretirement Plans, Expected Long-Term Rate Of Return, Average Of Actual Results, Period Of Measurement + References No definition available. + Details
Name: | arnc_PensionAndOtherPostretirementPlansExpectedLongTermRateOfReturnAverageOfActualResultsPeriodOfMeasurement
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Period of observation to determine average compensation increase. + References No definition available. + Details
Name: | arnc_PeriodOfObservationToDetermineAverageCompensationIncrease
Namespace Prefix: | arnc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + 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 (k)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + 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 (k)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + 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 (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status. + 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 (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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 Ultimate trend rate for health care cost for defined benefit postretirement plan. + 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 (l) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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 of payment for pension benefits. 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 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585 + Details
Name: | us-gaap_PensionContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=arnc_UnitedSteelworkersLaborAgreementMember
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: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanNameAxis=arnc_SalariedAndRetirementSavingsPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |