Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 5,667	$ 4,936	$ 2,919
Interest expense (income) on derivatives	34	(661)	(569)
Interest expense on debt and derivatives	5,701	4,275	2,350
Gains on debt denominated in foreign currencies	(96)	(80)	(614)
(Gains) losses on foreign currency swaps	(108)	(90)	805
Losses on U.S. dollar interest rate swaps	328	600	513
Total interest expense	$ 5,825	$ 4,705	$ 3,054