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Income Taxes - Schedule of Changes in Valuation Allowance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 1,291	$ 1,151	$ 1,252
Increase to allowance	772	180	102
Release of allowance	(209)	(42)	(70)
Acquisitions and divestitures (F)	(1)	29	(36)
Tax apportionment, tax rate and tax law changes	106	(15)	(67)
Foreign currency translation	(19)	(12)	(30)
Balance at end of year	$ 1,940	$ 1,291	$ 1,151

X

- Definition

Change in valuation allowance related to deferred state income taxes.

+ References

No definition available.

+ Details

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

X

- Definition

Deferred tax assets valuation acquisitions divestitures.

+ References

No definition available.

+ Details

Name:	arnc_DeferredTaxAssetsValuationAcquisitionsDivestitures
Namespace Prefix:	arnc_
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Balance Type:	debit
Period Type:	duration

X

- Definition

Deferred tax assets valuation foreign currency translation.

+ References

No definition available.

+ Details

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Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Deferred tax assets valuation release of allowance.

+ References

No definition available.

+ Details

Name:	arnc_DeferredTaxAssetsValuationReleaseOfAllowance
Namespace Prefix:	arnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32537-109319

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

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- References

No definition available.

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

X

- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=75116654&loc=d3e32123-109318

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