Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 467	$ 359
Interest income on derivatives	(16)	(2)
Interest expense on debt and derivatives, net	451	357
Total interest expense	448	307
Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Loss (gain) on non-hedge accounting debt denominated in foreign currencies	650	(218)
(Gain) loss on non-hedge accounting foreign currency swaps	(650)	188
Gain on U.S. dollar non-hedge accounting interest rate swaps	(3)	(20)
Hedge accounting derivatives [Member] | Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Loss (gain) on hedge accounting derivatives	7	(33)
Less hedged item: change in fair value of fixed rate debt denominated in a foreign currency	(7)	33
Ineffectiveness related to hedge accounting derivatives	0	0
Hedge accounting derivatives [Member] | Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments Gain Loss [Line Items]
Loss (gain) on hedge accounting derivatives	$ 7	$ (33)