Investments - Additional Information (Detail) $ in Millions			12 Months Ended
	Sep. 15, 2024 USD ($) shares	Feb. 15, 2022 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2024 CAD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Equity Method Investments [Line Items]
Dividends from equity investments			$ 37,000,000		$ 51,000,000	$ 127,000,000
Asset impairments			$ 5,000,000		50,000,000	58,000,000
Saudi Arabia Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture	25.10%
Sale of ownership interest under agreement exchange for issuance shares | shares	85,977,547
Percentage of joint venture ownership interest sold	25.10%
Sale Of Ownership Interest Unde Agreement Exchange for Cash	$ 150,000,000
Maaden Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Non-controlling interest, ownership percentage			25.10%
Equity investments			$ 544,000,000		533,000,000
ELYSIS TM Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Basis in investment, due to share of losses			0
Unrecognized losses			$ 67,000,000
Alcoa Corporation [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture			25.10%	25.10%
Equity investments			$ 544,000,000
Alcoa Corporation [Member] | Other Expenses (Income) [Member]
Schedule of Equity Method Investments [Line Items]
Charges recorded						$ 21,000,000
Adjustment recorded					$ 41,000,000
Alcoa Corporation [Member] | ELYSIS TM Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage			48.235%	48.235%
Contribution to joint venture			$ 152,000,000	$ 202
Overhead expenses			$ 3,000,000
RioTinto [Member] | ELYSIS TM Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest percentage			48.235%	48.235%
Investissement Quebec [Member] | ELYSIS TM Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Limited partner ownership interest percentage			3.53%	3.53%
Saudi Arabia [Member] | Ma'aden [Member] | Maaden Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture			74.90%	74.90%
Brazil [Member] | Mineracao Rio Do Norte S A
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Long-term Investments		$ 10,000,000
Asset impairments		58,000,000
Additional cash to be received upon satisfying post closing conditions		$ 30,000,000
Ma'aden Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture shareholders agreement period, years			30 years	30 years
Joint venture shareholders agreement, automatic extension additional period, years			20 years	20 years