v3.26.1
Financial Instruments and Commodity Contracts - Additional Information (Details)
metric_tons in Millions
 3 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
kt
MMBTU
metric_tons
gallon
Boe
Mar. 31, 2026
USD ($)
MMBTU
metric_tons
gallon
kt
Boe
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative assets (liabilities), at fair value, net $ 84,000,000 $ (585,000,000)
Expected reclassification from AOCI to earnings 64,000,000  
Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative assets (liabilities), at fair value, net 98,000,000 (446,000,000)
Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative assets (liabilities), at fair value, net $ (14,000,000) (139,000,000)
Aluminum Forward Sales Contracts | Designated as Hedging Instrument | Maximum    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years) 3 years  
Aluminum Forward Sales Contracts | Not Designated as Hedging Instrument | Maximum    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years) 1 year  
Copper Forward Contracts | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years) 1 year  
Fair value of derivative, asset $ 4,000,000 $ 1,000,000
Derivative, nonmonetary notional amount | kt 5,000,000 6,000,000
Midwest Premium ("MWP") Contracts | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years)   1 year
Fair value of derivative, liability $ 10,000,000 $ 69,000,000
Derivative, nonmonetary notional amount | kt 77,000,000 105,000,000
Midwest Premium ("MWP") Contracts | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years)   1 year
Fair value of derivative, liability $ 17,000,000 $ 14,000,000
Derivative, nonmonetary notional amount | kt 1,000,000 12,000,000
Currency Exchange Contracts | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Notional amount $ 1,800,000,000 $ 1,600,000,000
Derivative assets (liabilities), at fair value, net (21,000,000) (19,000,000)
Currency Exchange Contracts | Cash flow hedges | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Notional amount 1,200,000,000 1,100,000,000
Derivative assets (liabilities), at fair value, net (16,000,000) (11,000,000)
Currency Exchange Contracts | Net investment hedges | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Notional amount 127,000,000 128,000,000
Derivative assets (liabilities), at fair value, net $ 5,000,000 $ 4,000,000
Interest Rate Swap | Cash flow hedges | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, fixed interest rate 4.40% 4.40%
Notional amount $ 400,000,000 $ 400,000,000
Derivative assets (liabilities), at fair value, net (1,000,000) (3,000,000)
Natural Gas Swaps | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value of derivative, asset   $ 1,000,000
Fair value of derivative, liability $ 1,000,000  
Derivative, nonmonetary notional amount | MMBTU 1,000,000 1,000,000
Natural Gas Swaps | Not Designated as Hedging Instrument | Maximum    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years) 1 year  
Natural Gas Swaps | Cash flow hedges | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value of derivative, asset $ 2,000,000 $ 2,000,000
Derivative, nonmonetary notional amount | MMBTU 5,000,000 6,000,000
Diesel Fuel Forward Contracts | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years) 1 year  
Derivative, nonmonetary notional amount | metric_tons 1 1
Derivative assets (liabilities), at fair value, net $ 4,000,000 $ 9,000,000
Diesel Fuel Forward Contracts | Cash flow hedges | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value of derivative, asset $ 5,000,000 $ 7,000,000
Derivative, nonmonetary notional amount | gallon 5,000,000 6,000,000
Europe Premium Duty Paid ("ECDP") Contracts | Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative remaining maturity (in years)   1 year
Fair value of derivative, liability $ 6,000,000 $ 8,000,000
Derivative, nonmonetary notional amount | kt 33,000,000 47,000,000
Europe Premium Duty Paid ("ECDP") Contracts | Not Designated as Hedging Instrument    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value of derivative, liability $ 3,000,000 $ 12,000,000
Derivative, nonmonetary notional amount | kt 20,000,000 53,000,000
Forward Contracts [Member] | Designated as Hedging Instrument | South America    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative assets (liabilities), at fair value, net $ 1,000,000 $ 1,000,000
Derivative, Nonmonetary Notional Amount, Energy Measure | Boe 67,000 60,000
Forward Contracts [Member] | Not Designated as Hedging Instrument | South America    
Derivative Instruments, Gain (Loss) [Line Items]    
Derivative, Nonmonetary Notional Amount, Energy Measure | Boe 0 0