Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 1,265	$ 2,835	$ 1,345	$ 2,469
Total realized and unrealized gain (losses) recorded in revenue	3	10	(3)	20
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	4	0	(13)
Purchases	220	72	439	618
Settlements	(119)	(166)	(414)	(257)
Transfers into Level 3	152		152
Transfers out of Level 3	(169)	(357)	(169)	(439)
Fair value, end of period	1,350	2,398	1,350	2,398
Change in unrealized gains (losses) related to financial instruments held	2	0	2	0
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2		8	5
Total realized and unrealized gain (losses) recorded in revenue	1		(6)	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0		0	0
Purchases	2		7	0
Settlements	0		(4)	(8)
Transfers into Level 3	0		0
Transfers out of Level 3	0		0	0
Fair value, end of period	5	0	5	0
Change in unrealized gains (losses) related to financial instruments held	2		2	0
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2		8	5
Total realized and unrealized gain (losses) recorded in revenue	1		(6)	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0		0	0
Purchases	2		7	0
Settlements	0		(4)	(8)
Transfers into Level 3	0		0
Transfers out of Level 3	0		0	0
Fair value, end of period	5	0	5	0
Change in unrealized gains (losses) related to financial instruments held	2		2	0
Investment securities available-for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,263	2,835	1,337	2,464
Total realized and unrealized gain (losses) recorded in revenue	2	10	3	17
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	4	0	(13)
Purchases	218	72	432	618
Settlements	(119)	(166)	(410)	(249)
Transfers into Level 3	152		152
Transfers out of Level 3	(169)	(357)	(169)	(439)
Fair value, end of period	1,345	2,398	1,345	2,398
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	99	186	97	189
Total realized and unrealized gain (losses) recorded in revenue	0	1	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	3	2	0
Purchases	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0		0
Transfers out of Level 3	(99)	0	(99)	0
Fair value, end of period	0	190	0	190
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	771	1,813	905	1,764
Total realized and unrealized gain (losses) recorded in revenue	1	9	2	16
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	(2)	(1)	(13)
Purchases	199	19	354	132
Settlements	(120)	(129)	(410)	(189)
Transfers into Level 3	101		101
Transfers out of Level 3	0	0	0	0
Fair value, end of period	951	1,710	951	1,710
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	870	1,999	1,002	1,953
Total realized and unrealized gain (losses) recorded in revenue	1	10	2	17
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	1	1	(13)
Purchases	199	19	354	132
Settlements	(120)	(129)	(410)	(189)
Transfers into Level 3	101		101
Transfers out of Level 3	(99)	0	(99)	0
Fair value, end of period	951	1,900	951	1,900
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	59	127	32	174
Total realized and unrealized gain (losses) recorded in revenue	1	0	1	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	0	(1)	(1)
Purchases	0	53	31	107
Settlements	(16)	(16)	(20)	(34)
Transfers into Level 3	51		51
Transfers out of Level 3	(31)	(53)	(31)	(135)
Fair value, end of period	63	111	63	111
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	256	295	248	255
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	2	0	0
Purchases	0		5	29
Settlements	18	(7)	21	6
Transfers into Level 3	0		0
Transfers out of Level 3	0	(29)	0	(29)
Fair value, end of period	274	261	274	261
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	315	422	280	429
Total realized and unrealized gain (losses) recorded in revenue	1	0	1	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	2	(1)	(1)
Purchases	0	53	36	136
Settlements	2	(23)	1	(28)
Transfers into Level 3	51		51
Transfers out of Level 3	(31)	(82)	(31)	(164)
Fair value, end of period	337	372	337	372
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	39	32	39	33
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	0	0
Settlements	(1)	0	(1)	(1)
Transfers into Level 3	0		0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	38	33	38	33
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	39	82	16	39
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	0	0	23	50
Settlements	0	(14)	0	(21)
Transfers into Level 3	0		0
Transfers out of Level 3	(39)	0	(39)	0
Fair value, end of period	0	68	0	68
Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0		0	10
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	19		19	0
Settlements	0		0	(10)
Transfers into Level 3	0		0
Transfers out of Level 3	0		0	0
Fair value, end of period	$ 19	$ 0	$ 19	$ 0