Contingencies, Commitments and Other Liabilities (Details) € in Millions, $ in Millions					1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 15, 2023 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2023 EUR (€)	Jan. 01, 2023	Jul. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jul. 31, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) location	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2023 EUR (€)	Jul. 23, 2024 USD ($)	Jul. 23, 2024 EUR (€)	Jun. 26, 2020 transaction entity
Loss Contingencies [Line Items]
Number of cleanup locations | location										30
Remediation reserve balance						$ 17		$ 19		$ 19		$ 17
Remediation reserve balance, classified as a current liability						7		10		10		7
Payments related to remediation expenses applied against the reserve (less than in second quarter)								1		2
Income tax reserve								0	$ 0	0	$ 20
Guarantees of third party related to project financing								23		23
Combined fair value of guarantees						6		6		6		$ 6
Coverage limit						$ 80
Total amount committed under outstanding surety bonds								43		43
Surety bonds, amount outstanding								$ 21		$ 21
Termination notice period (in days)				30 days
Payment timing (in days)				120 days
Supplier Finance Program, Obligation, Current, Statement of Financial Position [Extensible Enumeration]						Accounts payable, trade (Q)		Accounts payable, trade (Q)		Accounts payable, trade (Q)		Accounts payable, trade (Q)
Supplier invoices subject to future payment						$ 258		$ 251		$ 251		$ 258
Letter of Credit
Loss Contingencies [Line Items]
Maximum borrowing capacity								91		91
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing						$ 1,131		1,131		$ 1,131		1,131
Lehman Brothers International (Europe) (“LBIE”) Claims
Loss Contingencies [Line Items]
Number of entities | entity																2
Number of interest rate swap transactions | transaction																2
Judgement from legal proceedings	$ 40
Payments for legal settlements					$ 25		$ 15
Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss		$ 17	€ 16
Income tax assessment, amount of penalties cancelled														$ 7	€ 7
Income tax reserve												$ 21	€ 19
Recurring Costs of Managing Hazardous Substances and Environmental Programs
Loss Contingencies [Line Items]
Percentage of cost of goods sold (as a percent)										1.00%
Income Tax and Interest | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss		10	9
Income Tax Penalties | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss		7	7
Additional Interest on Income Tax | Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Income tax assessment, estimate of possible loss		$ 2	€ 2
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding								48		$ 48
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding								$ 17		$ 17