Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	$ 5,447	$ 7,564
Recorded in Revenue, Assets	144	7
Recorded in Other Comprehensive Income, Assets	(11)	(5)
Purchases, Assets	483	93
Sales, Assets		(7)
Settlements, Assets	(358)	(366)
Transfers out of Level 3, Assets	(349)	(1,217)
Fair value as of end of period	5,356	6,069
Change in Unrealized Gains (Losses) Related to Financial Instruments Held as of period end	107	(7)
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	81	19
Recorded in Revenue, Assets	131	(11)
Recorded in Other Comprehensive Income, Assets	0	0
Purchases, Assets	36	7
Sales, Assets		0
Settlements, Assets	(63)	(9)
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	185	6
Change in Unrealized Gains (Losses) Related to Financial Instruments Held as of period end	107	(7)
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	81	19
Recorded in Revenue, Assets	131	(11)
Recorded in Other Comprehensive Income, Assets	0	0
Purchases, Assets	36	7
Sales, Assets		0
Settlements, Assets	(63)	(9)
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	185	6
Change in Unrealized Gains (Losses) Related to Financial Instruments Held as of period end	107	(7)
Categories of investments, marketable securities, available-for-sale securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	5,366	7,545
Recorded in Revenue, Assets	13	18
Recorded in Other Comprehensive Income, Assets	(11)	(5)
Purchases, Assets	447	86
Sales, Assets		(7)
Settlements, Assets	(295)	(357)
Transfers out of Level 3, Assets	(349)	(1,217)
Fair value as of end of period	5,171	6,063
Categories of investments, marketable securities, available-for-sale securities | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period		716
Recorded in Revenue, Assets		0
Recorded in Other Comprehensive Income, Assets		0
Purchases, Assets		0
Sales, Assets		0
Settlements, Assets		(5)
Transfers out of Level 3, Assets		(611)
Fair value as of end of period		100
Categories of investments, marketable securities, available-for-sale securities | Total asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	4,039	4,979
Recorded in Revenue, Assets	12	16
Recorded in Other Comprehensive Income, Assets	(11)	(3)
Purchases, Assets	0	6
Sales, Assets		0
Settlements, Assets	(150)	(282)
Transfers out of Level 3, Assets	0	(79)
Fair value as of end of period	3,890	4,637
Categories of investments, marketable securities, available-for-sale securities | Asset-backed securities, student loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	259	423
Recorded in Revenue, Assets	0	1
Recorded in Other Comprehensive Income, Assets	1	1
Purchases, Assets	0	0
Sales, Assets		0
Settlements, Assets	(3)	(13)
Transfers out of Level 3, Assets	0	(79)
Fair value as of end of period	257	333
Categories of investments, marketable securities, available-for-sale securities | Asset-backed securities, credit cards
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period		24
Recorded in Revenue, Assets		0
Recorded in Other Comprehensive Income, Assets		0
Purchases, Assets		0
Sales, Assets		0
Settlements, Assets		(24)
Transfers out of Level 3, Assets		0
Fair value as of end of period		0
Categories of investments, marketable securities, available-for-sale securities | Asset-backed securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	3,780	4,532
Recorded in Revenue, Assets	12	15
Recorded in Other Comprehensive Income, Assets	(12)	(4)
Purchases, Assets	0	6
Sales, Assets		0
Settlements, Assets	(147)	(245)
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	3,633	4,304
Categories of investments, marketable securities, available-for-sale securities | Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	666	1,637
Recorded in Revenue, Assets	1	2
Recorded in Other Comprehensive Income, Assets	1	(2)
Purchases, Assets	154	0
Sales, Assets		(1)
Settlements, Assets	(109)	(63)
Transfers out of Level 3, Assets	0	(499)
Fair value as of end of period	713	1,074
Categories of investments, marketable securities, available-for-sale securities | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	0	375
Recorded in Revenue, Assets	0	0
Recorded in Other Comprehensive Income, Assets	0	0
Purchases, Assets	43	0
Sales, Assets		0
Settlements, Assets	0	0
Transfers out of Level 3, Assets	0	(375)
Fair value as of end of period	43	0
Categories of investments, marketable securities, available-for-sale securities | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	295	798
Recorded in Revenue, Assets	1	2
Recorded in Other Comprehensive Income, Assets	0	(1)
Purchases, Assets	0	0
Sales, Assets		0
Settlements, Assets	(68)	(63)
Transfers out of Level 3, Assets	0	(124)
Fair value as of end of period	228	612
Categories of investments, marketable securities, available-for-sale securities | Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	371	464
Recorded in Revenue, Assets	0	0
Recorded in Other Comprehensive Income, Assets	1	(1)
Purchases, Assets	111	0
Sales, Assets		(1)
Settlements, Assets	(41)	0
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	442	462
Categories of investments, marketable securities, available-for-sale securities | State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	38	43
Recorded in Revenue, Assets	0	0
Recorded in Other Comprehensive Income, Assets	(1)	0
Purchases, Assets	0	0
Sales, Assets		0
Settlements, Assets	0	(1)
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	37	42
Categories of investments, marketable securities, available-for-sale securities | Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	614	162
Recorded in Revenue, Assets	0	0
Recorded in Other Comprehensive Income, Assets	0	0
Purchases, Assets	293	80
Sales, Assets		(6)
Settlements, Assets	(36)	(6)
Transfers out of Level 3, Assets	(349)	(28)
Fair value as of end of period	522	202
Categories of investments, marketable securities, available-for-sale securities | Other U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value as of beginning of period	9	8
Recorded in Revenue, Assets	0	0
Recorded in Other Comprehensive Income, Assets	0	0
Purchases, Assets	0	0
Sales, Assets		0
Settlements, Assets	0	0
Transfers out of Level 3, Assets	0	0
Fair value as of end of period	$ 9	$ 8