Accumulated Other Comprehensive Income/(Loss) - Components of Other Comprehensive Income/(Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Unrealized gains/(losses) on AFS securities:
Net change, unrealized gains/(losses) on AFS securities	$ 1,975	$ (4,070)	$ 3,303
Translation adjustments:
Net change after tax	(11)	(41)	(69)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax [Abstract]
Net change	44	(259)	69
Defined benefit pension and OPEB plans:
Net change, defined benefit pension and OPEB plans	(1,018)	1,467	(145)
Total other comprehensive income/(loss), after–tax	990	(2,903)	3,158
Unrealized gains/(losses) on investment securities
Unrealized gains/(losses) on AFS securities:
Net unrealized gains/(losses) arising during the period before tax	3,193	(5,987)	7,521
Net unrealized gains/(losses) arising during the period tax effect	(1,170)	2,323	(2,930)
Net unrealized gains/(losses) arising during the period after tax	2,023	(3,664)	4,591
Reclassification adjustment for realized (gains)/losses included in net income before tax	(77)	(667)	(2,110)
Reclassification adjustment for realized (gains)/losses included in net income tax effect	29	261	822
Reclassification adjustment for realized (gains)/losses included in net income after tax	(48)	(406)	(1,288)
Net change before tax	3,116	(6,654)	5,411
Net change tax effect	(1,141)	2,584	(2,108)
Net change, unrealized gains/(losses) on AFS securities	1,975	(4,070)	3,303
Translation adjustments, net of hedges
Translation adjustments:
Translation before tax	(1,638)	(807)	(26)
Translation tax effect	588	295	8
Translation after tax	(1,050)	(512)	(18)
Hedges before tax	1,698	773	(82)
Hedges tax effect	(659)	(302)	31
Hedges after tax	1,039	471	(51)
Net change before tax	60	(34)	(108)
Net change tax effect	(71)	(7)	39
Net change after tax	(11)	(41)	(69)
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	98	(525)	141
Net unrealized gains/(losses) arising during the period tax effect	(39)	206	(55)
Net unrealized gains/(losses) arising during the period after tax	59	(319)	86
Reclassification adjustment for realized (gains)/losses included in net income before tax	(24)	101	(28)
Reclassification adjustment for realized (gains)/losses included in net income tax effect	9	(41)	11
Reclassification adjustment for realized (gains)/losses included in net income after tax	(15)	60	(17)
Net change before tax	74	(424)	113
Net change tax effect	(30)	165	(44)
Net change	44	(259)	69
Defined benefit pension and OPEB plans
Defined benefit pension and OPEB plans:
Prior service credits arising during the period before tax	(53)	0	6
Prior service credits arising during the period tax effect	21	0	(2)
Prior service credits arising during the period after tax	(32)	0	4
Net gains/(losses) arising during the period before tax	(1,697)	2,055	(537)
Net gains/(losses) arising during the period tax effect	688	(750)	228
Net gains/(losses) arising during the period after tax	(1,009)	1,305	(309)
Reclassification adjustments included in net income, amortization of net loss before tax	72	321	324
Reclassification adjustments included in net income, amortization of net loss tax effect	(29)	(124)	(126)
Reclassification adjustments included in net income, amortization of net loss after tax	43	197	198
Reclassification adjustments included in net income, prior service costs/(credits) before tax	(44)	(43)	(41)
Reclassification adjustments included in net income, prior service costs/(credits) tax effect	17	17	16
Reclassification adjustments included in net income, prior service costs/(credits) after tax	(27)	(26)	(25)
Foreign exchange and other before tax	39	(14)	(21)
Foreign exchange and other tax effect	(32)	5	8
Foreign exchange and other after tax	7	(9)	(13)
Net change before tax	(1,683)	2,319	(269)
Net change tax effect	665	(852)	124
Net change, defined benefit pension and OPEB plans	(1,018)	1,467	(145)
Accumulated other comprehensive income/(loss) [Member]
Defined benefit pension and OPEB plans:
Total other comprehensive income/(loss) before tax	1,567	(4,793)	5,147
Total other comprehensive income/(loss) tax effect	(577)	1,890	(1,989)
Total other comprehensive income/(loss), after–tax	$ 990	$ (2,903)	$ 3,158