Fair Value - Schedule of Fair Value Measurements, Assets, Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	$ 1,288	$ 2,127
Total realized and unrealized gain (losses) recorded in revenue	(14)	1
Total realized and unrealized gain (losses) recorded in other comprehensive income	(10)	(27)
Purchases	1,544	865
Sales	0	(1,042)
Settlements	(381)	(361)
Transfers into Level 3	503	122
Transfers out of Level 3	(174)	(397)
Fair value, end of period	2,756	1,288
Change in unrealized gains (losses) related to financial instruments held	(11)	(3)
Derivative instruments, assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4	1
Total realized and unrealized gain (losses) recorded in revenue	(15)	(3)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	16	6
Sales	0	0
Settlements	(1)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	4	4
Change in unrealized gains (losses) related to financial instruments held	(11)	(3)
Foreign exchange contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	4	1
Total realized and unrealized gain (losses) recorded in revenue	(15)	(3)
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	0
Purchases	16	6
Sales	0	0
Settlements	(1)	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, end of period	4	4
Change in unrealized gains (losses) related to financial instruments held	(11)	(3)
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	123
Sales	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	(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	593	1,358
Total realized and unrealized gain (losses) recorded in revenue	1	4
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(7)
Purchases	1,065	351
Sales	0	(636)
Settlements	(342)	(268)
Transfers into Level 3	503	0
Transfers out of Level 3	0	(209)
Fair value, end of period	1,820	593
Asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	593	1,358
Total realized and unrealized gain (losses) recorded in revenue	1	4
Total realized and unrealized gain (losses) recorded in other comprehensive income	0	(7)
Purchases	1,065	351
Sales	0	(636)
Settlements	(342)	(268)
Transfers into Level 3	503	0
Transfers out of Level 3	0	(209)
Fair value, end of period	1,820	593
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	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
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	631	402
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(9)	(14)
Purchases	340	495
Sales	0	(310)
Settlements	(36)	(56)
Transfers into Level 3	0	114
Transfers out of Level 3	(39)	0
Fair value, end of period	887	631
Non-U.S. debt securities, other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	58	204
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(1)	(6)
Purchases	0	13
Sales	0	(59)
Settlements	0	(30)
Transfers into Level 3	0	0
Transfers out of Level 3	(12)	(64)
Fair value, end of period	45	58
Total non-U.S. debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	689	725
Total realized and unrealized gain (losses) recorded in revenue	0	0
Total realized and unrealized gain (losses) recorded in other comprehensive income	(10)	(20)
Purchases	340	508
Sales	0	(369)
Settlements	(36)	(86)
Transfers into Level 3	0	114
Transfers out of Level 3	(51)	(183)
Fair value, end of period	932	689
State and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	0	43
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
Sales	0	(37)
Settlements	0	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	(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	2	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	0
Sales	0	0
Settlements	(2)	(6)
Transfers into Level 3	0	8
Transfers out of Level 3	0	0
Fair value, end of period	0	2
Investment securities available-for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of period	1,284	2,126
Total realized and unrealized gain (losses) recorded in revenue	1	4
Total realized and unrealized gain (losses) recorded in other comprehensive income	(10)	(27)
Purchases	1,528	859
Sales	0	(1,042)
Settlements	(380)	(361)
Transfers into Level 3	503	122
Transfers out of Level 3	(174)	(397)
Fair value, end of period	$ 2,752	$ 1,284

Change in Unrealized Gains (Losses) Related to Financial Instruments, Assets, Held at Period End

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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-Subparagraph (c)(3)
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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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