Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 2,756	$ 1,288
Total realized and unrealized gain (losses) recorded in revenue	(6)	(14)
Total realized and unrealized gain (losses) recorded in other comprehensive income	27	(10)
Purchases	870	1,544
Sales	(95)	0
Settlements	(83)	(381)
Transfers into Level 3	50	503
Transfers out of Level 3	(3,503)	(174)
Fair value, end of period	16	2,756
Change in unrealized gains (losses) related to financial instruments held	(3)	(11)
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4	4
Total realized and unrealized gain (losses) recorded in revenue	(6)	(15)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	5	16
Sales	0	0
Settlements	(1)	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	2	4
Change in unrealized gains (losses) related to financial instruments held	(3)	(11)
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4	4
Total realized and unrealized gain (losses) recorded in revenue	(6)	(15)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	5	16
Sales	0	0
Settlements	(1)	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	2	4
Change in unrealized gains (losses) related to financial instruments held	(3)	(11)
Available for sale Investment 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
Total realized and unrealized gain (losses) recorded in other comprehensive income		0
Purchases		123
Sales		0
Settlements		0
Transfers into Level 3		0
Transfers out of Level 3		(123)
Fair value, end of period		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	1,820	593
Total realized and unrealized gain (losses) recorded in revenue	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	(10)	0
Purchases	864	1,065
Sales	(95)	0
Settlements	(77)	(342)
Transfers into Level 3	50	503
Transfers out of Level 3	(2,538)	0
Fair value, end of period	14	1,820
Asset-backed Securities, Other
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
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		0
Fair value, end of period		0
Asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,820	593
Total realized and unrealized gain (losses) recorded in revenue	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	(10)	0
Purchases	864	1,065
Sales	(95)	0
Settlements	(77)	(342)
Transfers into Level 3	50	503
Transfers out of Level 3	(2,538)	0
Fair value, end of period	14	1,820
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	887	631
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	35	(9)
Purchases	1	340
Sales	0	0
Settlements	(5)	(36)
Transfers into Level 3	0	0
Transfers out of Level 3	(918)	(39)
Fair value, end of period	0	887
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	45	58
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	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(47)	(12)
Fair value, end of period	0	45
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	932	689
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	37	(10)
Purchases	1	340
Sales	0	0
Settlements	(5)	(36)
Transfers into Level 3	0	0
Transfers out of Level 3	(965)	(51)
Fair value, end of period	0	932
State and political subdivisions
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
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		0
Fair value, end of period		0
Collateralized mortgage obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	2
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		(2)
Transfers into Level 3		0
Transfers out of Level 3		0
Fair value, end of period		0
Investment securities available-for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	2,752	1,284
Total realized and unrealized gain (losses) recorded in revenue	0	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	27	(10)
Purchases	865	1,528
Sales	(95)	0
Settlements	(82)	(380)
Transfers into Level 3	50	503
Transfers out of Level 3	(3,503)	(174)
Fair value, end of period	$ 14	$ 2,752