v3.25.4
Financial Instruments and Commodity Contracts - Additional Information (Details)
metric_tons in Millions
 3 Months Ended 9 Months Ended
Dec. 31, 2025
USD ($)
kt
MMBTU
metric_tons
gallon
Dec. 31, 2025
USD ($)
kt
MMBTU
metric_tons
gallon
Dec. 31, 2024
USD ($)
Mar. 31, 2025
USD ($)
metric_tons
kt
MMBTU
gallon
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative assets (liabilities), at fair value, net $ (277,000,000) $ (277,000,000)   $ 68,000,000
Expected reclassification from AOCI to earnings 223,000,000      
Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative assets (liabilities), at fair value, net (210,000,000) (210,000,000)   71,000,000
Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative assets (liabilities), at fair value, net $ (67,000,000) $ (67,000,000)   (3,000,000)
Aluminum Forward Sales Contracts | Designated as Hedging Instrument | Maximum        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative remaining maturity (in years) 3 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 1 year    
Copper Forward Contracts | Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative remaining maturity (in years) 1 year 1 year    
Fair value of derivative, asset $ 2,000,000 $ 2,000,000   $ 1,000,000
Derivative, nonmonetary notional amount | kt 3,000,000 3,000,000   4,000,000
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 $ 4,000,000 $ 4,000,000    
Derivative, nonmonetary notional amount | kt 58,000,000 58,000,000   0
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 $ 31,000,000 $ 31,000,000   $ 9,000,000
Derivative, nonmonetary notional amount | kt 104,000,000 104,000,000   29,000,000
Currency Exchange Contracts | Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Notional amount $ 1,300,000,000 $ 1,300,000,000   $ 1,500,000,000
Derivative assets (liabilities), at fair value, net 5,000,000 5,000,000   (5,000,000)
Currency Exchange Contracts | Cash flow hedges | Other Nonoperating Income (Expense)        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount excluded from effectiveness testing recognized in earnings based on changes in fair value   4,000,000    
Currency Exchange Contracts | Cash flow hedges | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Notional amount 1,000,000,000.0 1,000,000,000.0   1,100,000,000
Derivative assets (liabilities), at fair value, net 10,000,000 10,000,000   (22,000,000)
Currency Exchange Contracts | Net investment hedges | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Notional amount 131,000,000 131,000,000   261,000,000
Derivative assets (liabilities), at fair value, net $ 1,000,000 $ 1,000,000   $ 5,000,000
Interest Rate Swap | Cash flow hedges | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative, fixed interest rate 4.40% 4.40%   4.40%
Notional amount $ 400,000,000 $ 400,000,000   $ 400,000,000
Derivative assets (liabilities), at fair value, net (5,000,000) (5,000,000)   (5,000,000)
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 $ 1,000,000    
Derivative, nonmonetary notional amount | MMBTU 1,000,000 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 1 year    
Natural Gas Swaps | Cash flow hedges | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Fair value of derivative, asset $ 1,000,000 $ 1,000,000   $ 5,000,000
Derivative, nonmonetary notional amount | MMBTU 7,000,000 7,000,000   5,000,000
Diesel Fuel Forward Contracts | Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Derivative remaining maturity (in years) 1 year 1 year    
Derivative, nonmonetary notional amount | metric_tons 1 1   1
Derivative assets (liabilities), at fair value, net $ (1,000,000) $ (1,000,000)   $ 1,000,000
Diesel Fuel Forward Contracts | Cash flow hedges | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Fair value of derivative, liability $ 1,000,000 $ 1,000,000   $ 1,000,000
Derivative, nonmonetary notional amount | gallon 5,000,000 5,000,000   7,000,000
CapEx hedges | Cash flow hedges | Other Nonoperating Income (Expense)        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount excluded from effectiveness testing recognized in earnings based on changes in fair value   $ 2,000,000 $ 0