Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 2,398	$ 4,041	$ 2,469	$ 5,447
Total realized and unrealized gain (losses) recorded in revenue	13	17	33	97
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(26)	(9)	(44)
Purchases	553	169	1,170	632
Sales		(686)		(1,194)
Settlements	(569)	(443)	(828)	(1,157)
Transfers into Level 3				97
Transfers out of Level 3	(54)	(146)	(492)	(952)
Fair value, end of period	2,343	2,926	2,343	2,926
Change in unrealized gains (losses) related to financial instruments held	0	0	0	0
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		60	5	81
Total realized and unrealized gain (losses) recorded in revenue		(5)	3	49
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		1	0	17
Sales		0		0
Settlements		(35)	(8)	(126)
Transfers into Level 3				0
Transfers out of Level 3		0	0	0
Fair value, end of period	0	21	0	21
Change in unrealized gains (losses) related to financial instruments held		0	0	0
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		60	5	81
Total realized and unrealized gain (losses) recorded in revenue		(5)	3	49
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		1	0	17
Sales		0		0
Settlements		(35)	(8)	(126)
Transfers into Level 3				0
Transfers out of Level 3		0	0	0
Fair value, end of period	0	21	0	21
Change in unrealized gains (losses) related to financial instruments held		0	0	0
Investment securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2,398	3,981	2,464	5,366
Total realized and unrealized gain (losses) recorded in revenue	13	22	30	48
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(26)	(9)	(44)
Purchases	553	168	1,170	615
Sales		(686)		(1,194)
Settlements	(569)	(408)	(820)	(1,031)
Transfers into Level 3				97
Transfers out of Level 3	(54)	(146)	(492)	(952)
Fair value, end of period	2,343	2,905	2,343	2,905
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	25		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	25		325
Settlements	0		0
Transfers out of Level 3	0		(275)
Fair value, end of period	50		50
Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	190	234	189	259
Total realized and unrealized gain (losses) recorded in revenue	0	0	1	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(3)	2	(2)
Purchases	0	0	0	0
Sales		0		0
Settlements	0	(1)	0	(6)
Transfers into Level 3				0
Transfers out of Level 3	0	0	0	(21)
Fair value, end of period	192	230	192	230
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,710	2,933	1,764	3,780
Total realized and unrealized gain (losses) recorded in revenue	13	22	29	47
Total realized and unrealized gain (losses) recorded in other comprehensive income	(8)	(19)	(21)	(37)
Purchases	118	0	250	0
Sales		(686)		(1,106)
Settlements	(560)	(307)	(749)	(741)
Transfers into Level 3				0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	1,273	1,943	1,273	1,943
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,900	3,167	1,953	4,039
Total realized and unrealized gain (losses) recorded in revenue	13	22	30	47
Total realized and unrealized gain (losses) recorded in other comprehensive income	(6)	(22)	(19)	(39)
Purchases	118	0	250	0
Sales		(686)		(1,106)
Settlements	(560)	(308)	(749)	(747)
Transfers into Level 3				0
Transfers out of Level 3	0	0	0	(21)
Fair value, end of period	1,465	2,173	1,465	2,173
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	0	97	0	0
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	0	0	0
Purchases	90	0	90	43
Sales		0		0
Settlements	0	0	0	0
Transfers into Level 3				97
Transfers out of Level 3	0	(97)	0	(140)
Fair value, end of period	90	0	90	0
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	111	193	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	(1)	(1)	(1)
Purchases	90	168	196	168
Sales		0		0
Settlements	(9)	(83)	(43)	(169)
Transfers into Level 3				0
Transfers out of Level 3	(54)	0	(188)	(17)
Fair value, end of period	138	277	138	277
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	261	264	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	0	(1)	0	0
Purchases	194	0	223	111
Sales		0		0
Settlements	3	0	9	(32)
Transfers into Level 3				0
Transfers out of Level 3	0	0	(29)	(187)
Fair value, end of period	458	263	458	263
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	372	554	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	0	(2)	(1)	(1)
Purchases	374	168	509	322
Sales		0		0
Settlements	(6)	(83)	(34)	(201)
Transfers into Level 3				97
Transfers out of Level 3	(54)	(97)	(217)	(344)
Fair value, end of period	686	540	686	540
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	33	36	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	7	(1)	9	(2)
Purchases	0	0	0	0
Sales		0		0
Settlements	0	0	(2)	(1)
Transfers into Level 3				0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	40	35	40	35
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	68	215	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	1	(1)	2	(2)
Purchases	36	0	86	293
Sales				(88)
Settlements	(3)	(17)	(25)	(82)
Transfers into Level 3				0
Transfers out of Level 3	0	(49)	0	(587)
Fair value, end of period	102	148	102	148
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
Transfers out of Level 3		0	0	0
Fair value, end of period	$ 0	$ 9	$ 0	$ 9