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, 2012		Jun. 30, 2011
Derivatives, Hedging Activities and Interest Expense [Abstract]
Interest expense on debt	$ 337	[1]	$ 481	[1],[2]
Interest expense on hedge accounting derivatives	(27)	[1]	(81)	[1],[2]
Interest expense on non-hedge accounting foreign currency swaps	(67)	[1]	(132)	[1],[2]
Interest expense on non-hedge accounting interest rate swaps	103	[1]	180	[1],[2]
Interest expense on debt and derivatives	346	[1]	448	[1],[2]
Derivative Instruments, Gain (Loss) [Line Items]
Total interest expense	58		457
Relative fair value allocation of derivative credit valuation adjustments within interest expense
Ineffectiveness related to hedge accounting derivatives	1		2
Loss on non-hedge accounting foreign currency swaps	4		5
Loss on non-hedge accounting interest rate swaps	1		1
Total credit valuation adjustment allocated to interest expense	6		8
Interest expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on hedge accounting derivatives	122		(407)
Less hedged item: change in fair value of fixed rate debt	(125)		403
Ineffectiveness related to hedge accounting derivatives	(3)	[3]	(4)	[2],[3]
Total interest expense	58		457
Interest expense [Member] | Interest rate swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on hedge accounting derivatives	3	[3]	(7)	[2],[3]
Loss (gain) on foreign currency transactions	(44)	[3]	704	[2],[3]
Loss (gain) on other non-hedge accounting derivatives	(209)	[3]	118	[2],[3]
Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(Gain) loss on hedge accounting derivatives	119	[3]	(400)	[2],[3]
Loss (gain) on other non-hedge accounting derivatives	$ (32)	[3]	$ (809)	[2],[3]

[1] Amounts represent net interest settlements and changes in accruals

[2] Certain prior period amounts have been reclassified to conform to the current period presentation.

[3] Amounts exclude net interest settlements and changes in accruals.