Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 655	$ 601
Interest expense (income) on derivatives	12	(25)
Interest expense on debt and derivatives	667	576
Total interest expense	697	682
Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Losses (gains) on debt denominated in foreign currencies	15	(646)
(Gains) losses on foreign currency swaps	(108)	683
Losses on U.S. dollar interest rate swaps	$ 123	$ 69