Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 382	$ 495	$ 771	$ 1,071
Interest expense on derivatives	48	122	114	231
Interest expense on debt and derivatives	430	617	885	1,302
(Gains) losses on debt denominated in foreign currencies	(287)	500	(277)	1,048
Losses (gains) on foreign currency swaps	333	(503)	358	(1,096)
Total interest expense	423	495	709	1,043
Interest Expense
Derivative Instruments Gain Loss [Line Items]
Gains on U.S. dollar interest rate swaps	$ (53)	$ (119)	$ (257)	$ (211)