Fair Value Measurements - Fair Value Measurement (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets [Abstract]
Derivative contracts, at fair value (asset)	$ 1,439	$ 182
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value	970	1,190
Derivative contracts at fair value (liability)	172	1,224
Recurring measurement
Assets [Abstract]
Investments	6,758	9,732
Derivative contracts, at fair value (asset)	1,439	182
Assets, Fair Value Disclosure	8,197	9,914
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value	970	1,190
Other liabilities	85	13
Derivative contracts at fair value (liability)	172	1,224
Financial and Nonfinancial Liabilities, Fair Value Disclosure	1,227	2,427
Recurring measurement \| Level 1
Assets [Abstract]
Investments	6,400	9,448
Derivative contracts, at fair value (asset)	0	0
Assets, Fair Value Disclosure	6,400	9,448
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value	970	1,190
Other liabilities	0	0
Derivative contracts at fair value (liability)	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	970	1,190
Recurring measurement \| Level 2
Assets [Abstract]
Investments	157	281
Derivative contracts, at fair value (asset)	1,439	182
Assets, Fair Value Disclosure	1,596	463
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value	0	0
Other liabilities	83	7
Derivative contracts at fair value (liability)	172	1,224
Financial and Nonfinancial Liabilities, Fair Value Disclosure	255	1,231
Recurring measurement \| Level 3
Assets [Abstract]
Investments	201	3
Derivative contracts, at fair value (asset)	0	0
Assets, Fair Value Disclosure	201	3
Liabilities [Abstract]
Securities sold, not yet purchased, at fair value	0	0
Other liabilities	2	6
Derivative contracts at fair value (liability)	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 2	$ 6

Investments measured at fair value.

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- Definition

Unrealized Gain On Derivative Contracts

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
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-Publisher FASB
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- Definition

Fair value of obligations incurred from short sales.

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-Name Accounting Standards Codification
-Topic 940
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Fair value of financial and nonfinancial obligations.

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Fair value portion of other liabilities.

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