XML 66 R53.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Income Taxes - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Dec. 31, 2017 | Mar. 31, 2017
Income Tax Disclosure [Abstract] |  |  |
Effective income tax rate reconciliation, percent | 26.50% |  | 31.60%
Effective income tax rate reconciliation, including discrete items, percent | 28.10% |  | 33.50%
Discrete income tax expense | $ 2 |  | $ 1
Tax Cuts And Jobs Act of 2017, incomplete accounting, provisional income tax expense (benefit) |  | $ 272 |

X
- Definition Discrete Income Tax Expense + References No definition available. + Details
Name: | arnc_DiscreteIncomeTaxExpense
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Effective Income Tax Rate Reconciliation, Including Discrete Items, Percent + References No definition available. + Details
Name: | arnc_EffectiveIncomeTaxRateReconciliationIncludingDiscreteItemsPercent
Namespace Prefix: | arnc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tax Cuts And Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit) + References No definition available. + Details
Name: | arnc_TaxCutsAndJobsActof2017IncompleteAccountingProvisionalIncomeTaxExpenseBenefit
Namespace Prefix: | arnc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
Name: | us-gaap_EffectiveIncomeTaxRateContinuingOperations
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration