Contingencies and Commitments (Details) € in Millions, $ in Millions		1 Months Ended				3 Months Ended				9 Months Ended
	Jun. 15, 2023 USD ($) installment	Jul. 31, 2024 USD ($)	Jul. 31, 2023 USD ($)	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 EUR (€)	Jun. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) location	Sep. 30, 2022 USD ($)	Mar. 31, 2023 EUR (€)	Jun. 26, 2020 derivative entity
Loss Contingencies [Line Items]
Number of cleanup locations | location										30
Remediation reserve balance					$ 16	$ 17				$ 17
Remediation reserve balance, classified as a current liability					6	6				6
Payments related to remediation expenses applied against the reserve						2			$ 1	4	$ 1
Income tax reserve						0			0	20	0
Judgement from legal proceedings				$ 74
Reversal of previously recorded litigation amount								$ 25		25
Guarantees of third party related to project financing						20				20
Combined fair value of guarantees					6	6				6
Coverage limit					80
Total amount committed under outstanding surety bonds						42				42
Surety bonds, amount outstanding						21				21
Bank Loan Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount						116				116
Other Noncurrent Liabilities and Deferred Credits | Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing					$ 1,040	1,040				1,040
Lehman Brothers International (Europe) (“LBIE”) Claims
Loss Contingencies [Line Items]
Judgement from legal proceedings	$ 40
Number of entities | entity													2
Number of derivative transactions | derivative													2
Amount reserved									$ 65		$ 65
Number of installment payments | installment	2
Payments for legal settlements			$ 15
Lehman Brothers International (Europe) (“LBIE”) Claims | Subsequent Event | Forecast
Loss Contingencies [Line Items]
Payments for legal settlements		$ 25
Foreign Tax Authority | Ministry of the Economy, Finance and Industry, France | Tax Years 2010 Through 2012
Loss Contingencies [Line Items]
Assessment amount				$ 19								€ 18
Income tax reserve						20	€ 19
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding						52				52
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding						$ 17				$ 17
Maximum | Recurring Costs of Managing Hazardous Substances and Environmental Programs
Loss Contingencies [Line Items]
Percentage of cost of goods sold (as a percent)										1.00%