Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 2,123	$ 1,501	$ 1,288	$ 2,127
Total realized and unrealized gain (losses) recorded in revenue	(1)	(1)	(2)	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(29)	(8)	(30)	(25)
Purchases	104	79	914	778
Sales	0		0	(983)
Settlements	(98)	(245)	(275)	(306)
Transfers into Level 3	230	54	446	122
Transfers out of Level 3	(162)	(64)	(174)	(397)
Fair value, end of period	2,167	1,316	2,167	1,316
Change in unrealized gains (losses) related to financial instruments held	0	(2)	0	(2)
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	11	7	4	1
Total realized and unrealized gain (losses) recorded in revenue	(1)	(2)	(3)	(3)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0	0	0
Purchases	5	3	14	4
Sales	0		0	0
Settlements	(1)	(6)	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	14	2	14	2
Change in unrealized gains (losses) related to financial instruments held	0	(2)	0	(2)
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	11	7	4	1
Total realized and unrealized gain (losses) recorded in revenue	(1)	(2)	(3)	(3)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0	0	0
Purchases	5	3	14	4
Sales	0		0	0
Settlements	(1)	(6)	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	14	2	14	2
Change in unrealized gains (losses) related to financial instruments held	0	(2)	0	(2)
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	123		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	0		123
Sales	0		0
Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	(123)		(123)
Fair value, end of period	0		0
Asset-backed securities, collateralized loan obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,222	851	593	1,358
Total realized and unrealized gain (losses) recorded in revenue	0	1	1	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(2)	0	(5)
Purchases	33	0	620	319
Sales	0		0	(636)
Settlements	(97)	(239)	(272)	(219)
Transfers into Level 3	230	0	446	0
Transfers out of Level 3	0	0	0	(209)
Fair value, end of period	1,388	611	1,388	611
Asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,222	851	593	1,358
Total realized and unrealized gain (losses) recorded in revenue	0	1	1	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(2)	0	(5)
Purchases	33	0	620	319
Sales	0		0	(636)
Settlements	(97)	(239)	(272)	(219)
Transfers into Level 3	230	0	446	0
Transfers out of Level 3	0	0	0	(209)
Fair value, end of period	1,388	611	1,388	611
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				119
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				0
Transfers into Level 3				0
Transfers out of Level 3				(119)
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	721	474	631	402
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(27)	(5)	(28)	(14)
Purchases	66	76	157	455
Sales	0		0	(310)
Settlements	0	0	0	(56)
Transfers into Level 3	0	46	0	114
Transfers out of Level 3	(39)	0	(39)	0
Fair value, end of period	721	591	721	591
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	46	169	58	204
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(2)	(1)	(2)	(6)
Purchases	0	0	0	0
Sales	0		0	0
Settlements	0	0	0	(30)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(64)	(12)	(64)
Fair value, end of period	44	104	44	104
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	767	643	689	725
Total realized and unrealized gain (losses) recorded in revenue	0	0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(29)	(6)	(30)	(20)
Purchases	66	76	157	455
Sales	0		0	(310)
Settlements	0	0	0	(86)
Transfers into Level 3	0	46	0	114
Transfers out of Level 3	(39)	(64)	(51)	(183)
Fair value, end of period	765	695	765	695
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period				43
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				(37)
Settlements				(1)
Transfers into Level 3				0
Transfers out of Level 3				(5)
Fair value, end of period		0		0
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period		0	2	0
Total realized and unrealized gain (losses) recorded in revenue		0	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income		0	0	0
Purchases		0	0	0
Sales			0	0
Settlements		0	(2)	0
Transfers into Level 3		8	0	8
Transfers out of Level 3		0	0	0
Fair value, end of period	0	8	0	8
Investment securities available-for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2,112	1,494	1,284	2,126
Total realized and unrealized gain (losses) recorded in revenue	0	1	1	3
Total realized and unrealized gain (losses) recorded in other comprehensive income	(29)	(8)	(30)	(25)
Purchases	99	76	900	774
Sales	0		0	(983)
Settlements	(97)	(239)	(274)	(306)
Transfers into Level 3	230	54	446	122
Transfers out of Level 3	(162)	(64)	(174)	(397)
Fair value, end of period	$ 2,153	$ 1,314	$ 2,153	$ 1,314