Derivative instruments - Impact on Statements of Income, Fair Value Hedges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Gains/(losses) recorded in income
Derivatives	$ 2,613	$ 6,006	$ 6,599	$ 6,160
Hedged items	(2,340)	(5,637)	(5,844)	(5,160)
Total income statement impact	273	369	755	1,000
Income statement impact due to:
Hedge ineffectiveness	5	37	(8)	137
Excluded components	268	332	763	863
Interest rate
Gains/(losses) recorded in income
Derivatives	1,298	(286)	363	1,035
Hedged items	(1,071)	651	390	(17)
Total income statement impact	227	365	753	1,018
Income statement impact due to:
Hedge ineffectiveness	8	27	6	99
Excluded components	219	338	747	919
Foreign exchange
Gains/(losses) recorded in income
Derivatives	1,012	6,008	5,369	5,222
Hedged items	(998)	(6,052)	(5,360)	(5,421)
Total income statement impact	14	(44)	9	(199)
Income statement impact due to:
Hedge ineffectiveness	0	0	0	0
Excluded components	14	(44)	9	(199)
Commodity
Gains/(losses) recorded in income
Derivatives	303	284	867	(97)
Hedged items	(271)	(236)	(874)	278
Total income statement impact	32	48	(7)	181
Income statement impact due to:
Hedge ineffectiveness	(3)	10	(14)	38
Excluded components	$ 35	$ 38	$ 7	$ 143