Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 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	10	144
Total realized and unrealized gain (losses) recorded in other comprehensive income	(16)	(11)
Purchases	545	483
Settlements	(91)	(358)
Transfers out of Level 3	(82)	(349)
Fair value, end of period	2,835	5,356
Change in unrealized gains (losses) related to financial instruments held	0	107
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	3	131
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	0	36
Settlements	(8)	(63)
Transfers out of Level 3	0	0
Fair value, end of period	0	185
Change in unrealized gains (losses) related to financial instruments held	0	107
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	3	131
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	0	36
Settlements	(8)	(63)
Transfers out of Level 3	0	0
Fair value, end of period	0	185
Change in unrealized gains (losses) related to financial instruments held	0	107
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	7	13
Total realized and unrealized gain (losses) recorded in other comprehensive income	(16)	(11)
Purchases	545	447
Settlements	(83)	(295)
Transfers out of Level 3	(82)	(349)
Fair value, end of period	2,835	5,171
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	189	259
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(3)	1
Purchases	0	0
Settlements	0	(3)
Transfers out of Level 3	0	0
Fair value, end of period	186	257
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	7	12
Total realized and unrealized gain (losses) recorded in other comprehensive income	(11)	(12)
Purchases	113	0
Settlements	(60)	(147)
Transfers out of Level 3	0	0
Fair value, end of period	1,813	3,633
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		4,039
Total realized and unrealized gain (losses) recorded in revenue	7	12
Total realized and unrealized gain (losses) recorded in other comprehensive income	(14)	(11)
Purchases	113	0
Settlements	(60)	(150)
Transfers out of Level 3	0	0
Fair value, end of period	1,999	3,890
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
Total realized and unrealized gain (losses) recorded in revenue		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		43
Settlements		0
Transfers out of Level 3		0
Fair value, end of period		43
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	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	53	0
Settlements	(18)	(68)
Transfers out of Level 3	(82)	0
Fair value, end of period	127	228
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	(2)	1
Purchases	29	111
Settlements	13	(41)
Transfers out of Level 3	0	0
Fair value, end of period	295	442
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	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	1
Purchases	82	154
Settlements	(5)	(109)
Transfers out of Level 3	(82)	0
Fair value, end of period	422	713
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	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(1)
Purchases	0	0
Settlements	(1)	0
Transfers out of Level 3	0	0
Fair value, end of period	33	37
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	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	50	293
Settlements	(7)	(36)
Transfers out of Level 3	0	(349)
Fair value, end of period	82	522
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
Settlements	(10)	0
Transfers out of Level 3	0	0
Fair value, end of period	0	$ 9
Recurring | Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 1,953