Collateralized Transactions - Collateral Received (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Collateralized Agreements [Abstract]
Collateral received with right to sell or repledge	$ 699,097	$ 639,610
Collateral that was sold or repledged	$ 559,790	$ 487,983

Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it is permitted by contract or custom to sell or re-pledge to counterparties as collateral.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_CustomerSecuritiesForWhichEntityHasRightToSellOrRepledgeFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant