Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 2,469	$ 5,447
Total realized and unrealized gain (losses) recorded in revenue	41	104
Total realized and unrealized gain (losses) recorded in other comprehensive income	(9)	(61)
Purchases	1,394	706
Sales	(148)	(1,193)
Settlements	(1,370)	(1,390)
Transfers into Level 3		111
Transfers out of Level 3	(1,032)	(1,255)
Fair value, end of period	1,345	2,469
Change in unrealized gains (losses) related to financial instruments held	5	(4)
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	5	81
Total realized and unrealized gain (losses) recorded in revenue	9	48
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	3	9
Sales	0	0
Settlements	(9)	(133)
Transfers into Level 3		0
Transfers out of Level 3	0	0
Fair value, end of period	8	5
Change in unrealized gains (losses) related to financial instruments held	5	(4)
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	5	81
Total realized and unrealized gain (losses) recorded in revenue	9	48
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	3	9
Sales	0	0
Settlements	(9)	(133)
Transfers into Level 3		0
Transfers out of Level 3	0	0
Fair value, end of period	8	5
Change in unrealized gains (losses) related to financial instruments held	5	(4)
Investment securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2,464	5,366
Total realized and unrealized gain (losses) recorded in revenue	32	56
Total realized and unrealized gain (losses) recorded in other comprehensive income	(9)	(61)
Purchases	1,391	697
Sales	(148)	(1,193)
Settlements	(1,361)	(1,257)
Transfers into Level 3		111
Transfers out of Level 3	(1,032)	(1,255)
Fair value, end of period	1,337	2,464
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	325
Sales	0
Settlements	0
Transfers out of Level 3	(325)
Fair value, end of period	0	0
Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	189	259
Total realized and unrealized gain (losses) recorded in revenue	1	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	3	(4)
Purchases	0	0
Sales	0	0
Settlements	0	(6)
Transfers into Level 3		0
Transfers out of Level 3	(96)	(61)
Fair value, end of period	97	189
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,764	3,780
Total realized and unrealized gain (losses) recorded in revenue	31	53
Total realized and unrealized gain (losses) recorded in other comprehensive income	(23)	(50)
Purchases	469	0
Sales	(82)	(1,105)
Settlements	(1,254)	(914)
Transfers into Level 3		0
Transfers out of Level 3	0	0
Fair value, end of period	905	1,764
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,953	4,039
Total realized and unrealized gain (losses) recorded in revenue	32	54
Total realized and unrealized gain (losses) recorded in other comprehensive income	(20)	(54)
Purchases	469	0
Sales	(82)	(1,105)
Settlements	(1,254)	(920)
Transfers into Level 3		0
Transfers out of Level 3	(96)	(61)
Fair value, end of period	1,002	1,953
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	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	90	43
Sales	0	0
Settlements	0	0
Transfers into Level 3		97
Transfers out of Level 3	(90)	(140)
Fair value, end of period	0	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	174	295
Total realized and unrealized gain (losses) recorded in revenue	0	2
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(1)
Purchases	196	249
Sales	0	0
Settlements	(60)	(190)
Transfers into Level 3		4
Transfers out of Level 3	(278)	(185)
Fair value, end of period	32	174
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	255	371
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(1)
Purchases	222	111
Sales	0	0
Settlements	(7)	(39)
Transfers into Level 3		0
Transfers out of Level 3	(222)	(187)
Fair value, end of period	248	255
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	429	666
Total realized and unrealized gain (losses) recorded in revenue	0	2
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(2)
Purchases	508	403
Sales	0	0
Settlements	(67)	(229)
Transfers into Level 3		101
Transfers out of Level 3	(590)	(512)
Fair value, end of period	280	429
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	33	38
Total realized and unrealized gain (losses) recorded in revenue	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	9	(3)
Purchases	0	0
Sales	0	0
Settlements	(3)	(3)
Transfers into Level 3		0
Transfers out of Level 3	0	0
Fair value, end of period	39	33
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	39	614
Total realized and unrealized gain (losses) recorded in revenue	0	(1)
Total realized and unrealized gain (losses) recorded in other comprehensive income	2	(2)
Purchases	89	294
Sales	(66)	(88)
Settlements	(27)	(105)
Transfers into Level 3		0
Transfers out of Level 3	(21)	(673)
Fair value, end of period	16	39
Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	10	9
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
Sales	0	0
Settlements	(10)	0
Transfers into Level 3		10
Transfers out of Level 3	0	(9)
Fair value, end of period	$ 0	$ 10