Derivatives and Other Financial Instruments - Schedule of Outstanding Quantities of Derivative Instruments (Detail) - Level 1 [Member] kt in Thousands, € in Millions, kr in Millions, R$ in Millions, $ in Millions, $ in Millions	Mar. 31, 2025 EUR (€) MWh kt	Mar. 31, 2025 NOK (kr) MWh kt	Mar. 31, 2025 BRL (R$) MWh kt	Mar. 31, 2025 AUD ($) MWh kt	Mar. 31, 2025 CAD ($) MWh kt	Mar. 31, 2024 EUR (€) MWh kt	Mar. 31, 2024 NOK (kr) MWh kt	Mar. 31, 2024 BRL (R$) MWh kt	Mar. 31, 2024 AUD ($) MWh kt	Mar. 31, 2024 CAD ($) MWh kt
Foreign Exchange Buy Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liabilities	€ 163	kr 20	R$ 160	$ 41	$ 0	€ 79	kr 102	R$ 450	$ 0	$ 26
Foreign Exchange Buy Forwards Undesignated [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liabilities | €	852					0
Foreign Exchange Sell Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative Liabilities | €	€ 11					€ 17
Commodity Sell Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Outstanding quantities of derivative instruments | kt	458	458	458	458	458	44	44	44	44	44
Commodity Buy Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Outstanding quantities of derivative instruments | kt	173	173	173	173	173	101	101	101	101	101
Outstanding energy derivative instruments | MWh	2	2	2	2	2	0	0	0	0	0