Applicable margin on LIBOR loans.

No definition available.

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- Definition

Debt covenants net leverage ratio.

+ References

No definition available.

+ Details

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- Definition

Debt Covenants Net Leverage Ratio After Year Four

+ References

No definition available.

+ Details

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- Definition

Debt covenants net leverage ratio after year three.

+ References

No definition available.

+ Details

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- Definition

Debt Instrument, Number of Extensions

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Debt Weighted Average Maturity Term

+ References

No definition available.

+ Details

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- Definition

Extended additional maturity period.

+ References

No definition available.

+ Details

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- Definition

Line of credit facility, term.

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Maximum Increase in Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum Indebtedness for Other Principal Amounts

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate, outstanding borrowings.

+ References

No definition available.

+ Details

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 470
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-Section 50
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+ Details

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- 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

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Balance Type:	credit
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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Balance Type:	debit
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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

+ References

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Balance Type:	debit
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- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Debt - Credit Facilities (Details)				12 Months Ended
Debt - Credit Facilities (Details)	Jun. 29, 2018	Sep. 16, 2016 USD ($)	Jul. 25, 2014 USD ($)	Dec. 31, 2018 USD ($) extension	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 715,000,000
Arconic
Debt Instrument [Line Items]
Proceeds from lines of credit				$ 600,000,000
Line of credit facility, repayment					$ 810,000,000	$ 1,950,000,000
Weighted-average interest rate				3.30%	2.60%	1.90%
Weighted-average maturity days				46 days	46 days	49 days
Maximum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans				1.50%
Minimum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans				0.50%
Revolving Credit Agreement
Debt Instrument [Line Items]
Revolving credit facility, term			5 years
Revolving Credit Agreement \| Prior to Amendment
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings			$ 4,000,000,000
Revolving Credit Agreement \| After Amendment
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings		$ 3,000,000,000
Maximum increase in borrowing capacity		$ 500,000,000
Ratio of indebtedness to consolidated EBITDA		4.50%
Ratio of indebtedness to consolidated EBITDA, after December 31, 2019				4.00%
Consolidated Net Debt to consolidated EBITDA ratio				3.50%
Number of extensions allowable under terms of the Credit Facility \| extension				2
Extension of maturity period	1 year
Amount of principal indebtedness that would cause default				$ 100,000,000
Revolving Credit Agreement \| Maximum
Debt Instrument [Line Items]
Fees paid to maintain credit facility				0.25%
Revolving Credit Agreement \| Letter of Credit \| After Amendment
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings		$ 1,000,000,000
Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings				$ 0	$ 0
Amounts borrowed under the credit agreement				0	$ 0	$ 0
Expected Maturity Date Year 2019
Debt Instrument [Line Items]
Aggregate outstanding principal amount				465,000,000
Expected Maturity Date Year 2020
Debt Instrument [Line Items]
Aggregate outstanding principal amount				$ 250,000,000