Accumulated other comprehensive income/(loss) (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
Unrealized gains/(losses) on AFS securities:
Net change, unrealized gains/(losses) on AFS securities	$ (291)		$ (141)	$ (1,621)	$ 1,928
Translation adjustments:
Net change after tax	(5)		3	(12)	13
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Net change	(106)		(58)	51	69
Defined benefit pension and OPEB plans:
Net change, defined benefit pension and OPEB plans	51		24	144	57
Total other comprehensive income, after–tax	(351)		(172)	(1,438)	2,067
Net losses reclassified from AOCI to other income		$ 150
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period before tax	(430)		(283)	(2,548)	3,116
Net unrealized gains/(losses) arising during the period tax effect	160		146	1,008	(1,158)
Net unrealized gains/(losses) arising during the period after tax	(270)		(137)	(1,540)	1,958
Reclassification adjustment for realized (gains)/losses included in net income before tax	(33)		(6)	(129)	(48)
Reclassification adjustment for realized (gains)/losses included in net income tax effect	12		2	48	18
Reclassification adjustment for realized (gains)/losses included in net income after tax	(21)		(4)	(81)	(30)
Net change before tax	(463)		(289)	(2,677)	3,068
Net change tax effect	172		148	1,056	(1,140)
Net change, unrealized gains/(losses) on AFS securities	(291)		(141)	(1,621)	1,928
Translation adjustments, net of hedges
Translation adjustments:
Translation before tax	(912)		(1,133)	(1,645)	(761)
Translation tax effect	340		416	601	274
Translation after tax	(572)		(717)	(1,044)	(487)
Hedges before tax	908		1,185	1,651	823
Hedges tax effect	(341)		(465)	(619)	(323)
Hedges after tax	567		720	1,032	500
Net change before tax	(4)		52	6	62
Net change tax effect	(1)		(49)	(18)	(49)
Net change after tax	(5)		3	(12)	13
Cash flow hedges
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Net unrealized gains/(losses) arising during the period before tax	(175)		(66)	(104)	149
Net unrealized gains/(losses) arising during the period tax effect	66		27	38	(60)
Net unrealized gains/(losses) arising during the period after tax	(109)		(39)	(66)	89
Reclassification adjustment for realized (gains)/losses included in net income before tax	5		(31)	187	(33)
Reclassification adjustment for realized (gains)/losses included in net income tax effect	(2)		12	(70)	13
Reclassification adjustment for realized (gains)/losses included in net income after tax	3		(19)	117	(20)
Net change before tax	(170)		(97)	83	116
Net change tax effect	64		39	(32)	(47)
Net change	(106)		(58)	51	69
Defined benefit pension and OPEB plans
Defined benefit pension and OPEB plans:
Net gains/(losses) arising during the period before tax	0		(1)	101	87
Net gains/(losses) arising during the period tax effect	0		0	(39)	(34)
Net gains/(losses) arising during the period after tax	0		(1)	62	53
Reclassification adjustments included in net income, amortization of net loss before tax	71		18	212	55
Reclassification adjustments included in net income, amortization of net loss tax effect	(27)		(8)	(80)	(23)
Reclassification adjustments included in net income, amortization of net loss after tax	44		10	132	32
Reclassification adjustments included in net income, prior service costs/(credits) before tax	(9)		(10)	(27)	(32)
Reclassification adjustments included in net income, prior service costs/(credits) tax effect	3		4	10	13
Reclassification adjustments included in net income, prior service costs/(credits) after tax	(6)		(6)	(17)	(19)
Foreign exchange and other before tax	20		34	20	15
Foreign exchange and other tax effect	(7)		(13)	(53)	(24)
Foreign exchange and other after tax	13		21	(33)	(9)
Net change before tax	82		41	306	125
Net change tax effect	(31)		(17)	(162)	(68)
Net change, defined benefit pension and OPEB plans	51		24	144	57
Accumulated other comprehensive income
Defined benefit pension and OPEB plans:
Total other comprehensive income/(loss) before tax	(555)		(293)	(2,282)	3,371
Total other comprehensive income/(loss) tax effect	204		121	844	(1,304)
Total other comprehensive income, after–tax	$ (351)		$ (172)	$ (1,438)	$ 2,067