v3.26.1
Financial Instruments and Commodity Contracts (Details Textual)
gallon in Millions, MMBTU in Millions
 12 Months Ended
Mar. 31, 2026
USD ($)
kt
gallon
Boe
MMBTU
Mar. 31, 2025
USD ($)
kt
gallon
MMBTU
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (585,000,000) $ 68,000,000
Expected reclassification of gains (losses) from AOCI to earnings (508,000,000)  
Derivative Liability 642,000,000 54,000,000
Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) (139,000,000) (3,000,000)
Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) (446,000,000) 71,000,000
Aluminum Forward Sales Contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ 0 0
Aluminum Forward Sales Contracts | Derivatives not designated as hedging instruments: | Maximum    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Remaining Maturity 1 year  
Aluminum Forward Sales Contracts | Cash flow hedges | Derivatives designated as hedging instruments: | Maximum    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Remaining Maturity 3 years  
Metal forward contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (1,000,000) $ (1,000,000)
Derivative, Remaining Maturity 1 year 1 year
Midwest Premium ("MWP") Contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | kt 12,000,000 29,000,000
Derivative, Remaining Maturity   1 year
Derivative Liability $ 14,000,000 $ 9,000,000
Midwest Premium ("MWP") Contracts | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | kt 105,000,000 0
Derivative, Remaining Maturity   1 year
Derivative Liability $ 69,000,000  
Europe Premium Duty Paid ("ECDP") Contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | kt 53,000,000  
Derivative Liability $ 12,000,000  
Europe Premium Duty Paid ("ECDP") Contracts | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | kt 47,000,000 0
Derivative, Remaining Maturity 1 year 1 year
Derivative Liability $ 8,000,000  
Currency exchange contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) (19,000,000) $ (5,000,000)
Derivative, Notional Amount 1,600,000,000 1,500,000,000
Currency exchange contracts | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Notional Amount 128,000,000 261,000,000
Currency exchange contracts | Cash flow hedges    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Notional Amount 1,100,000,000  
Currency exchange contracts | Cash flow hedges | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) (11,000,000) (22,000,000)
Interest rate swap contracts | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Notional Amount $ 400,000,000 400,000,000
Derivative, Average Fixed Interest Rate 4.40%  
Interest rate swap contracts | Cash flow hedges | Derivatives designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (3,000,000) (5,000,000)
Fuel | Derivatives not designated as hedging instruments: | North America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (7,000,000) $ (1,000,000)
Fuel | Derivatives not designated as hedging instruments: | Europe    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 1  
Fuel | Derivatives designated as hedging instruments: | North America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | gallon 6 7
Fuel | Derivatives designated as hedging instruments: | Europe    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ 9,000,000 $ 1,000,000
Derivative, Remaining Maturity 1 year  
Natural Gas Swaps | Derivatives not designated as hedging instruments: | North America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (1,000,000) $ (1,000,000)
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 1  
Natural Gas Swaps | Derivatives not designated as hedging instruments: | South America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 0  
Derivative, Remaining Maturity 1 year 1 year
Natural Gas Swaps | Derivatives designated as hedging instruments: | North America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability) $ (2,000,000) $ (5,000,000)
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU 6 5
Forward Contracts | Derivatives not designated as hedging instruments: | South America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative asset (liability)   $ 1,000,000
Derivative, Nonmonetary Notional Amount, Energy Measure | Boe 60,000  
Forward Contracts | Derivatives designated as hedging instruments: | South America    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount, Energy Measure | Boe 0  
LME Copper and Zinc Forward Contracts | Derivatives not designated as hedging instruments:    
Financial Instruments And Commodity Contracts [Abstract]    
Derivative, Nonmonetary Notional Amount | kt 6,000,000 4,000,000