Divestitures - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2021	Sep. 30, 2022	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Business Disposition [Line Items]
Net gain from asset sales				$ (7)	$ 132
Payments against the reserve		$ 7		17		$ 23
Eastalco Aluminum Smelter Site [Member] | Maryland [Member]
Business Disposition [Line Items]
Total consideration	$ 100
Net gain from asset sales	90
Net cash received	94
Net gain from asset sales after tax	$ 89
Warrick Rolling Mill [Member]
Business Disposition [Line Items]
Estimated liabilities for future site separation commitment charge				5
Warrick Rolling Mill [Member] | Held for Sale [Member]
Business Disposition [Line Items]
Total consideration			$ 670
Net gain from asset sales			30
Assumption of other postretirement benefit liabilities			$ 69
Remaining reserve		57		57
Payments against the reserve		$ 13		$ 22