Contingencies and Commitments - Additional Information (Detail) $ in Millions			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 15, 2024 USD ($)	Jul. 18, 2024 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) Project	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Loss Contingencies [Line Items]
Liabilities incurred				$ 20	$ 13	$ 38	$ 39
Payments against the reserve			$ 14	19	30	42	55
Reversals of previously recorded liabilities					11	(1)	1
Environmental remediation reserve balance, current			$ 58		$ 58		$ 66
Environmental Loss Contingency, Current, Statement of Financial Position [Extensible Enumeration]			Other Liabilities, Current		Other Liabilities, Current		Other Liabilities, Current
Active or future remediation for significant sites			$ 182		$ 182		$ 211
Accrued environmental reserves			240		$ 240		268	$ 284
Payment for settlements to former employees		$ 5
Subsequent Event [Member]
Loss Contingencies [Line Items]
Stipulated settlement payment amount	$ 5
Intalco Aluminum Smelter [Member]
Loss Contingencies [Line Items]
Liabilities incurred						14
Massena, New York [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period					4 years
Massena, New York [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period					8 years
Longview, Washington [Member] | Intalco Aluminum Smelter [Member] | Ongoing Remediation Work [Member]
Loss Contingencies [Line Items]
Liabilities incurred				13		13
Addy, Washington [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period					3 years
Addy, Washington [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Environmental remediation work completion period					5 years
Ferndale, Washington [Member]
Loss Contingencies [Line Items]
Post-closure maintenance and monitoring period					5 years
Other Sites [Member]
Loss Contingencies [Line Items]
Liabilities incurred				$ 7		7
Number of remediation projects | Project					32
Accrued environmental reserves			58		$ 58		$ 57
Other Sites [Member] | Cost of Goods Sold [Member] | Ongoing Remediation Work [Member]
Loss Contingencies [Line Items]
Liabilities incurred						$ 4
Closed sites [Member] | Restructuring and Other Charges, Net [Member]
Loss Contingencies [Line Items]
Reversals of previously recorded liabilities			(11)		(11)
Closed sites [Member] | Restructuring and Other Charges, Net [Member] | Ongoing Remediation Work [Member]
Loss Contingencies [Line Items]
Liabilities incurred			4		5
Closed sites [Member] | Cost of Goods Sold [Member] | Ongoing Remediation Work [Member]
Loss Contingencies [Line Items]
Reversals of previously recorded liabilities			(8)		(8)
Operating and Previously Closed Sites [Member] | Ongoing Remediation Work [Member]
Loss Contingencies [Line Items]
Liabilities incurred			$ 12		$ 13