Divestitures - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Business Disposition [Line Items]
Net gain from asset sales				$ (18)	$ (10)	$ 354
Payments against the reserve				55	26	23
Rockdale Smelter Curtailment [Member] | Texas [Member]
Business Disposition [Line Items]
Total consideration		$ 240				$ 240
Net cash received		230
Net gain from asset sales		$ 202
Eastalco Aluminum Smelter Site [Member] | Maryland [Member]
Business Disposition [Line Items]
Total consideration			$ 100
Net cash received			94
Net gain from asset sales			90
Net gain from asset sales after tax			$ 89
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
Estimated liabilities for future site separation commitment charge				17	8
Payments against the reserve				52	$ 37
Remaining reserve				$ 11