Derivatives, Hedging Activities and Interest Expense (Effect of Derivative Instruments on Income Statement) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivatives, Hedging Activities and Interest Expense [Abstract]
Interest expense on debt	$ 298	$ 320	$ 619	$ 638
Interest expense on hedge accounting derivatives	(10)	(25)	(25)	(49)
Interest expense on non-hedge accounting foreign currency swaps	(37)	(54)	(92)	(105)
Interest expense on non-hedge accounting interest rate swaps	27	61	64	127
Interest expense on debt and derivatives	278	302	566	611
Derivative Instruments, Loss (Gain) [Line Items]
Total interest expense	215	314	345	850
Interest expense [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss (gain) on hedge accounting derivatives	69	(56)	73	(6)
Less hedged item: change in fair value of fixed rate debt	(69)	55	(73)	4
Ineffectiveness related to hedge accounting derivatives	0	(1)	0	(2)
(Gain) loss on non-hedge accounting foreign currency transactions	(867)	352	(787)	(98)
Total interest expense	215	314	345	850
Interest expense [Member] | Interest rate swap [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss (gain) on hedge accounting derivatives	5	4	10	10
(Gain) loss on non-hedge accounting interest rate swaps	(62)	(4)	(145)	108
Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss (gain) on hedge accounting derivatives	64	(60)	63	(16)
Loss (gain) on non-hedge accounting foreign currency swaps	$ 866	$ (335)	$ 711	$ 231