Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	$ 70,070	$ 94,913
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	5,447	7,564
Total realized and unrealized gain (losses) recorded in revenue	104	110
Total realized and unrealized gain (losses) recorded in other comprehensive income	(61)	(28)
Purchases	706	1,198
Sales	(1,193)	(82)
Settlements	(1,390)	(1,504)
Transfers into Level 3	111	161
Transfers out of Level 3	(1,255)	(1,972)
Fair value, end of period	2,469	5,447
Change in unrealized gains (losses) related to financial instruments held	(4)	44
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	81	19
Total realized and unrealized gain (losses) recorded in revenue	48	36
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	9	36
Sales	0	0
Settlements	(133)	(10)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	5	81
Change in unrealized gains (losses) related to financial instruments held	(4)	44
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	81	19
Total realized and unrealized gain (losses) recorded in revenue	48	36
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	9	36
Sales	0	0
Settlements	(133)	(10)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	5	81
Change in unrealized gains (losses) related to financial instruments held	(4)	44
Investment securities available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	5,366	7,545
Total realized and unrealized gain (losses) recorded in revenue	56	74
Total realized and unrealized gain (losses) recorded in other comprehensive income	(61)	(28)
Purchases	697	1,162
Sales	(1,193)	(82)
Settlements	(1,257)	(1,494)
Transfers into Level 3	111	161
Transfers out of Level 3	(1,255)	(1,972)
Fair value, end of period	2,464	5,366
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	716
Total realized and unrealized gain (losses) recorded in revenue		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		168
Sales		0
Settlements		(14)
Transfers into Level 3		0
Transfers out of Level 3		(870)
Fair value, end of period		0
Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	259	423
Total realized and unrealized gain (losses) recorded in revenue	1	2
Total realized and unrealized gain (losses) recorded in other comprehensive income	(4)	1
Purchases	0	24
Sales	0	(75)
Settlements	(6)	(37)
Transfers into Level 3	0	0
Transfers out of Level 3	(61)	(79)
Fair value, end of period	189	259
Asset-backed securities, credit cards
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	24
Total realized and unrealized gain (losses) recorded in revenue		0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		0
Sales		0
Settlements		(24)
Transfers into Level 3		0
Transfers out of Level 3		0
Fair value, end of period		0
Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	3,780	4,532
Total realized and unrealized gain (losses) recorded in revenue	53	65
Total realized and unrealized gain (losses) recorded in other comprehensive income	(50)	(28)
Purchases	0	282
Sales	(1,105)	0
Settlements	(914)	(1,071)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	1,764	3,780
Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4,039	4,979
Total realized and unrealized gain (losses) recorded in revenue	54	67
Total realized and unrealized gain (losses) recorded in other comprehensive income	(54)	(27)
Purchases	0	306
Sales	(1,105)	(75)
Settlements	(920)	(1,132)
Transfers into Level 3	0	0
Transfers out of Level 3	(61)	(79)
Fair value, end of period	1,953	4,039
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	375
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	43	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	97	0
Transfers out of Level 3	(140)	(375)
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	295	798
Total realized and unrealized gain (losses) recorded in revenue	2	6
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	(1)
Purchases	249	0
Sales	0	0
Settlements	(190)	(272)
Transfers into Level 3	4	76
Transfers out of Level 3	(185)	(312)
Fair value, end of period	174	295
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	371	464
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	1
Purchases	111	55
Sales	0	(1)
Settlements	(39)	(41)
Transfers into Level 3	0	85
Transfers out of Level 3	(187)	(192)
Fair value, end of period	255	371
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	666	1,637
Total realized and unrealized gain (losses) recorded in revenue	2	6
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	0
Purchases	403	55
Sales	0	(1)
Settlements	(229)	(313)
Transfers into Level 3	101	161
Transfers out of Level 3	(512)	(879)
Fair value, end of period	429	666
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	38	43
Total realized and unrealized gain (losses) recorded in revenue	1	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	(3)	(3)
Purchases	0	0
Sales	0	0
Settlements	(3)	(3)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	33	38
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	614	162
Total realized and unrealized gain (losses) recorded in revenue	(1)	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	1
Purchases	294	633
Sales	(88)	(6)
Settlements	(105)	(32)
Transfers into Level 3	0	0
Transfers out of Level 3	(673)	(144)
Fair value, end of period	39	614
Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	9	8
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
Sales	0	0
Settlements	0	0
Transfers into Level 3	10	0
Transfers out of Level 3	(9)	0
Fair value, end of period	10	9
Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	70,070	94,913
Recurring | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	18,165	20,714
Recurring | Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	7,176	12,460
Recurring | Asset-backed securities, credit cards
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	1,341	3,053
Recurring | Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	1,764	4,145
Recurring | Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	10,700	20,609
Recurring | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	7,071	9,606
Recurring | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	3,267	3,226
Recurring | Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	4,834	5,428
Recurring | Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	19,527	22,169
Recurring | State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	9,746	10,820
Recurring | Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	2,987	5,339
Recurring | Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	2,624	4,109
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	2,464	5,366
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	0	0
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	189	259
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Asset-backed securities, credit cards
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	0	0
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	1,764	3,780
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	1,953	4,039
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	0	0
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	174	295
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	255	371
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	429	666
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	33	38
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	39	614
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Recurring | Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available for sale	$ 10	$ 9