Derivatives, Hedging Activities and Interest Expense (Effect of Derivative Instruments on Income Statement) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Derivatives, Hedging Activities and Interest Expense [Abstract]
Interest expense on debt	$ 321	$ 318
Interest expense on hedge accounting derivatives	(15)	(24)
Interest expense on non-hedge accounting foreign currency swaps	(55)	(51)
Interest expense on non-hedge accounting interest rate swaps	37	66
Interest expense on debt and derivatives	288	309
Derivative Instruments, Loss (Gain) [Line Items]
Total interest expense	130	536
Interest expense [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss on hedge accounting derivatives	4	50
Less hedged item: change in fair value of fixed rate debt	(4)	(51)
Ineffectiveness related to hedge accounting derivatives	0	(1)
Loss (gain) on non-hedge accounting foreign currency transactions	80	(450)
Total interest expense	130	536
Interest expense [Member] | Interest rate swap [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss on hedge accounting derivatives	5	6
(Gain) loss on non-hedge accounting interest rate swaps	(83)	112
Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments, Loss (Gain) [Line Items]
Loss on hedge accounting derivatives	(1)	44
Gain (loss) on non-hedge accounting foreign currency swaps	$ (155)	$ 566