Derivative instruments - Impact on Statements of Income, Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gains/(losses) recorded in income and other comprehensive income/(loss)
Net losses reclassified from AOCI to other income		$ 150
Recognition of gain (loss) related to cash flow hedges in Income				$ 11
Terminated Cash Flows
Gains/(losses) recorded in income and other comprehensive income/(loss)
Maximum length of time hedged in forecasted transactions				8 years
Open Cash Flow Hedges
Gains/(losses) recorded in income and other comprehensive income/(loss)
Maximum length of time hedged in forecasted transactions				2 years
Cash Flow Hedging
Gains/(losses) recorded in income and other comprehensive income/(loss)
Derivatives – effective portion reclassified from AOCI to income	$ (5)		$ 31	$ (187)	$ 33
Hedge ineffectiveness recorded directly in income	0		0	0	0
Total income statement impact	(5)		31	(187)	33
Derivatives – effective portion recorded in OCI	(175)		(66)	(104)	149
Total change in OCI for period	(170)		(97)	83	116
Cash Flow Hedging | Interest rate
Gains/(losses) recorded in income and other comprehensive income/(loss)
Derivatives – effective portion reclassified from AOCI to income	14		(12)	(113)	(48)
Hedge ineffectiveness recorded directly in income	0		0	0	0
Total income statement impact	14		(12)	(113)	(48)
Derivatives – effective portion recorded in OCI	(70)		26	(90)	160
Total change in OCI for period	(84)		38	23	208
Cash Flow Hedging | Foreign exchange
Gains/(losses) recorded in income and other comprehensive income/(loss)
Derivatives – effective portion reclassified from AOCI to income	(19)		43	(74)	81
Hedge ineffectiveness recorded directly in income	0		0	0	0
Total income statement impact	(19)		43	(74)	81
Derivatives – effective portion recorded in OCI	(105)		(92)	(14)	(11)
Total change in OCI for period	$ (86)		$ (135)	$ 60	$ (92)