Derivatives, Hedging Activities and Interest Expense - Components of Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt	$ 377	$ 307	$ 736	$ 630
Interest (income) expense on derivatives	(5)	6	(7)	(5)
Interest expense on debt and derivatives, net	372	313	729	625
Total interest expense	297	203	604	711
Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Loss (gain) on non-hedge accounting debt denominated in foreign currencies	156	(200)	(62)	154
(Gain) loss on non-hedge accounting foreign currency swaps	(156)	141	32	(93)
(Gain) loss on U.S. dollar non-hedge accounting interest rate swaps	(75)	(50)	(95)	26
Hedge accounting derivatives [Member] | Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
(Gain) loss on hedge accounting derivatives	(4)	2	(37)	17
Less hedged item: change in fair value of fixed rate debt denominated in a foreign currency	4	(3)	37	(18)
Ineffectiveness related to hedge accounting derivatives	0	(1)	0	(1)
Hedge accounting derivatives [Member] | Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments Gain Loss [Line Items]
(Gain) loss on hedge accounting derivatives	$ (4)	$ 2	$ (37)	$ 17