XML 147 R102.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Inventories - Additional Information (Details) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2018 USD ($) plant | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Inventory [Line Items] |  |  |
Inventories valued on a LIFO basis |  | $ 1,257 | $ 1,292
Total inventories valued on an average-cost basis |  | $ 445 | $ 530
Engineered Products and Forgings |  |  |
Inventory [Line Items] |  |  |
Inventory adjustment recorded in cost of goods sold and inventories | $ 23 |  |
Number of plants with inventory adjustments | plant | 1 |  |

X
- Definition Number Of Plants + References No definition available. + Details
Name: | arnc_NumberOfPlants
Namespace Prefix: | arnc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of inventory reserves for last-in first-out (LIFO) and other inventory valuation methods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=116847112&loc=d3e4492-108314 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.6(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_InventoryAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount by which inventory stated at last-in first-out (LIFO) is less than (in excess of) inventory stated at other inventory cost methods. + 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 210.5-02.6(c)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_InventoryLIFOReserve
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition The amount of LIFO (last in first out) inventory present at the reporting date when inventory is also valued using different valuation methods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766 + Details
Name: | us-gaap_LIFOInventoryAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=arnc_EngineeredProductsAndForgingsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |