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Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jul. 28, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Subsequent Event [Line Items]
Restructuring and other charges		$ 33	$ 37	$ 40	$ 39
Subsequent Event [Member] | Curtailed Anode Facility [Member] | Lake Charles, Louisiana, United States [Member]
Subsequent Event [Line Items]
Asset impairment	$ 20
Facility closure expected period	1 year
Subsequent Event [Member] | Curtailed Anode Facility [Member] | Lake Charles, Louisiana, United States [Member] | Minimum [Member]
Subsequent Event [Line Items]
Restructuring and other charges	$ 25
Asset retirement obligation	5
Subsequent Event [Member] | Curtailed Anode Facility [Member] | Lake Charles, Louisiana, United States [Member] | Maximum [Member]
Subsequent Event [Line Items]
Restructuring and other charges	30
Asset retirement obligation	$ 10

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- Definition

Facility closure expected period.

+ References

No definition available.

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- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Includes expenses related to certain asset retirement obligations.

+ References

No definition available.

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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