Cash and Securities Segregated Under Federal Regulations and Other Requirements	9 Months Ended
Sep. 30, 2019
Brokers and Dealers [Abstract]
Cash and Securities Segregated Under Federal Regulations and Other Requirements	Cash and Securities Segregated Under Federal Regulations and Other Requirements As of September 30, 2019 and December 31, 2018, $1.0 billion and $1.2 billion, respectively, of U.S. Treasury Bills were segregated in a special reserve bank custody account for the exclusive benefit of our brokerage customers under Rule 15c3-3 of the Exchange Act.

The entire disclosure for assets that are restricted in their use, generally by contractual agreements or regulatory requirements. This would include, but not limited to, a description of the restricted assets and the terms of the restriction.

No definition available.

Name:	us-gaap_RestrictedAssetsDisclosureTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration