XML 69 R56.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Earnings Per Share - Schedule of Anti Dilutive Securities Excluded From Computation of Weighted Average Shares Outstanding (Detail) - $ / shares shares in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Mandatory convertible preferred stock |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Number of anti-dilutive securities (in shares) | 0 | 0
Convertible notes |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Number of anti-dilutive securities (in shares) | 0 | 0
Stock options |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Number of anti-dilutive securities (in shares) | 6 | 0
Weighted average exercise price of options (in usd per share) | $ 30.75 |
Stock awards |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Number of anti-dilutive securities (in shares) | 0 | 4

X
- Definition The weighted average exercise price of stock options whose individual exercise prices were greater than the average market price of an entity's common stock during the period. + References No definition available. + Details
Name: | arnc_WeightedAverageExercisePriceOfUnderwaterOptions
Namespace Prefix: | arnc_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
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_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=arnc_MandatoryConvertibleNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=arnc_ConvertibleNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis=arnc_StockAwardsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |