Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 1,345	$ 2,469
Total realized and unrealized gain (losses) recorded in revenue	(6)	10
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(16)
Purchases	219	545
Settlements	(295)	(91)
Transfers out of Level 3		(82)
Fair value, end of period	1,265	2,835
Change in unrealized gains (losses) related to financial instruments held	(3)	0
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	8	5
Total realized and unrealized gain (losses) recorded in revenue	(7)	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	5	0
Settlements	(4)	(8)
Transfers out of Level 3		0
Fair value, end of period	2	0
Change in unrealized gains (losses) related to financial instruments held	(3)	0
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	8	5
Total realized and unrealized gain (losses) recorded in revenue	(7)	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	5	0
Settlements	(4)	(8)
Transfers out of Level 3		0
Fair value, end of period	2	0
Change in unrealized gains (losses) related to financial instruments held	(3)	0
Investment securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,337	2,464
Total realized and unrealized gain (losses) recorded in revenue	1	7
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(16)
Purchases	214	545
Settlements	(291)	(83)
Transfers out of Level 3		(82)
Fair value, end of period	1,263	2,835
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		0
Total realized and unrealized gain (losses) recorded in revenue		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		300
Settlements		0
Transfers out of Level 3		0
Fair value, end of period		300
Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	97	189
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(3)
Purchases	0	0
Settlements	0	0
Transfers out of Level 3		0
Fair value, end of period	99	186
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	905	1,764
Total realized and unrealized gain (losses) recorded in revenue	1	7
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(11)
Purchases	155	113
Settlements	(290)	(60)
Transfers out of Level 3		0
Fair value, end of period	771	1,813
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,002	1,953
Total realized and unrealized gain (losses) recorded in revenue	1	7
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(14)
Purchases	155	113
Settlements	(290)	(60)
Transfers out of Level 3		0
Fair value, end of period	870	1,999
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	32	174
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	31	53
Settlements	(4)	(18)
Transfers out of Level 3		(82)
Fair value, end of period	59	127
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	248	255
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(2)
Purchases	5	29
Settlements	3	13
Transfers out of Level 3		0
Fair value, end of period	256	295
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	280	429
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(2)
Purchases	36	82
Settlements	(1)	(5)
Transfers out of Level 3		(82)
Fair value, end of period	315	422
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	39	33
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	0
Settlements	0	(1)
Transfers out of Level 3		0
Fair value, end of period	39	32
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	16	39
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	23	50
Settlements	0	(7)
Transfers out of Level 3		0
Fair value, end of period	$ 39	82
Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		10
Total realized and unrealized gain (losses) recorded in revenue		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		0
Settlements		(10)
Transfers out of Level 3		0
Fair value, end of period		$ 0