Fair Value Measurements - Derivative Assets and Liabilities on Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Jun. 30, 2024	Mar. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivative Asset, Master Netting Adjustment	$ (60)	$ (32)
Fair value of derivative, asset	33	14
Derivative Liability, Master Netting Adjustment	60	32
Derivative Liability	(146)	(117)
Level 2 Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	93	46
Liabilities	(206)	(149)
Level 2 Instruments | Aluminum Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	69	33
Liabilities	(149)	(112)
Level 2 Instruments | Currency Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	23	11
Liabilities	(54)	(30)
Level 2 Instruments | Energy Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	1	2
Liabilities	(2)	(5)
Level 2 Instruments | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Assets	0	0
Liabilities	$ (1)	$ (2)