Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 2,835	$ 5,356	$ 2,469	$ 5,447
Total realized and unrealized gain (losses) recorded in revenue	10	(83)	20	71
Total realized and unrealized gain (losses) recorded in other comprehensive income	4	(7)	(13)	(18)
Purchases	72	10	618	476
Sales		(508)		(508)
Settlements	(166)	(366)	(257)	(718)
Transfers into Level 3		97		97
Transfers out of Level 3	(357)	(458)	(439)	(806)
Fair value, end of period	2,398	4,041	2,398	4,041
Change in unrealized gains (losses) related to financial instruments held	0	(30)	0	12
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		185	5	81
Total realized and unrealized gain (losses) recorded in revenue		(96)	3	45
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		10	0	29
Sales		0		0
Settlements		(39)	(8)	(95)
Transfers into Level 3		0		0
Transfers out of Level 3		0	0	0
Fair value, end of period	0	60	0	60
Change in unrealized gains (losses) related to financial instruments held		(30)	0	12
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		185	5	81
Total realized and unrealized gain (losses) recorded in revenue		(96)	3	45
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		10	0	29
Sales		0		0
Settlements		(39)	(8)	(95)
Transfers into Level 3		0		0
Transfers out of Level 3		0	0	0
Fair value, end of period	0	60	0	60
Change in unrealized gains (losses) related to financial instruments held		(30)	0	12
Investment securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2,835	5,171	2,464	5,366
Total realized and unrealized gain (losses) recorded in revenue	10	13	17	26
Total realized and unrealized gain (losses) recorded in other comprehensive income	4	(7)	(13)	(18)
Purchases	72	0	618	447
Sales		(508)		(508)
Settlements	(166)	(327)	(249)	(623)
Transfers into Level 3		97		97
Transfers out of Level 3	(357)	(458)	(439)	(806)
Fair value, end of period	2,398	3,981	2,398	3,981
US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	300		0
Total realized and unrealized gain (losses) recorded in revenue	0		0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0		0
Purchases	0		300
Settlements	0		0
Transfers out of Level 3	(275)		(275)
Fair value, end of period	25		25
Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	186	257	189	259
Total realized and unrealized gain (losses) recorded in revenue	1	0	1	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	3	0	0	1
Purchases	0	0	0	0
Sales		0		0
Settlements	0	(1)	0	(5)
Transfers into Level 3		0		0
Transfers out of Level 3	0	(22)	0	(21)
Fair value, end of period	190	234	190	234
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,813	3,633	1,764	3,780
Total realized and unrealized gain (losses) recorded in revenue	9	13	16	25
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	(6)	(13)	(18)
Purchases	19	0	132	0
Sales		(420)		(420)
Settlements	(129)	(287)	(189)	(434)
Transfers into Level 3		0		0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	1,710	2,933	1,710	2,933
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,999	3,890	1,953	4,039
Total realized and unrealized gain (losses) recorded in revenue	10	13	17	25
Total realized and unrealized gain (losses) recorded in other comprehensive income	1	(6)	(13)	(17)
Purchases	19	0	132	0
Sales		(420)		(420)
Settlements	(129)	(288)	(189)	(439)
Transfers into Level 3		0		0
Transfers out of Level 3	0	(22)	0	(21)
Fair value, end of period	1,900	3,167	1,900	3,167
Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		43		0
Total realized and unrealized gain (losses) recorded in revenue		0		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0		0
Purchases		0		43
Sales		0		0
Settlements		0		0
Transfers into Level 3		97		97
Transfers out of Level 3		(43)		(43)
Fair value, end of period		97		97
Non-U.S. debt securities, asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	127	228	174	295
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0	(1)	0
Purchases	53	0	107	0
Sales		0		0
Settlements	(16)	(18)	(34)	(86)
Transfers into Level 3		0		0
Transfers out of Level 3	(53)	(17)	(135)	(17)
Fair value, end of period	111	193	111	193
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	295	442	255	371
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	0	0	1
Purchases	0	0	29	111
Sales		0		0
Settlements	(7)	9	6	(32)
Transfers into Level 3		0		0
Transfers out of Level 3	(29)	(187)	(29)	(187)
Fair value, end of period	261	264	261	264
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	422	713	429	666
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	0	(1)	1
Purchases	53	0	136	154
Sales		0		0
Settlements	(23)	(9)	(28)	(118)
Transfers into Level 3		97		97
Transfers out of Level 3	(82)	(247)	(164)	(247)
Fair value, end of period	372	554	372	554
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	32	37	33	38
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	1	0	1	(1)
Purchases	0	0	0	0
Sales		0		0
Settlements	0	(1)	(1)	(1)
Transfers into Level 3		0		0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	33	36	33	36
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	82	522	39	614
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(1)	0	(1)
Purchases	0	0	50	293
Sales		(88)		(88)
Settlements	(14)	(29)	(21)	(65)
Transfers into Level 3		0		0
Transfers out of Level 3	0	(189)	0	(538)
Fair value, end of period	68	215	68	215
Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		9	10	9
Total realized and unrealized gain (losses) recorded in revenue		0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		0	0	0
Sales		0		0
Settlements		0	(10)	0
Transfers into Level 3		0		0
Transfers out of Level 3		0	0	0
Fair value, end of period	$ 0	$ 9	$ 0	$ 9