Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 397	$ 334	$ 1,133	$ 964
Interest expense (income) on derivatives	2	1	(5)	(4)
Interest expense on debt and derivatives, net	399	335	1,128	960
Total interest expense	701	277	1,305	988
Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Gain on non-hedge accounting debt denominated in foreign currencies	(907)	(222)	(969)	(68)
Loss on non-hedge accounting foreign currency swaps	1,127	263	1,159	170
Loss (gain) on U.S. dollar non-hedge accounting interest rate swaps	82	(98)	(13)	(72)
Hedge accounting derivatives [Member] | Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Loss on hedge accounting derivatives	62	6	25	23
Less hedged item: change in fair value of fixed rate debt denominated in a foreign currency	(62)	(7)	(25)	(25)
Ineffectiveness related to hedge accounting derivatives	0	(1)	0	(2)
Hedge accounting derivatives [Member] | Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments Gain Loss [Line Items]
Loss on hedge accounting derivatives	$ 62	$ 6	$ 25	$ 23