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Cash and Securities Segregated Under Federal Regulations and Other Requirements
9 Months Ended
Sep. 30, 2020
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, 2020 and December 31, 2019, $1.9 billion and $1.1 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.