Derivatives, Hedging Activities and Interest Expense - Derivative Activity Impact on Consolidated Statement of Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments Gain Loss [Line Items]
Interest expense on debt									$ 1,213	$ 1,262	$ 1,330
Interest income on hedge accounting derivatives									(43)	(85)	(103)
Interest income on non-hedge accounting foreign currency swaps									(147)	(202)	(258)
Interest expense on non-hedge accounting interest rate swaps									123	210	359
Interest expense on debt and derivatives, net									1,146	1,185	1,328
Total interest expense	230	161	215	130	104	386	314	536	736	1,340	940
Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Gain on non-hedge accounting foreign currency transactions									(2,375)	(45)	(430)
Loss on non-hedge accounting foreign currency swaps									2,248	185	431
(Gain) loss on non-hedge accounting interest rate swaps									(282)	18	(379)
Hedge accounting derivatives [Member] | Interest expense [Member]
Derivative Instruments Gain Loss [Line Items]
Loss on hedge accounting derivatives									141	28	289
Less hedged item: change in fair value of fixed rate debt									(142)	(31)	(299)
Ineffectiveness related to hedge accounting derivatives									(1)	(3)	(10)
Hedge accounting derivatives [Member] | Interest expense [Member] | Interest rate swap [Member]
Derivative Instruments Gain Loss [Line Items]
Loss on hedge accounting derivatives									19	20	15
Hedge accounting derivatives [Member] | Interest expense [Member] | Foreign currency swaps [Member]
Derivative Instruments Gain Loss [Line Items]
Loss on hedge accounting derivatives									$ 122	$ 8	$ 274