If a loss remains after a subsidiary’s capital is applied, DTC/NSCC/FICC could access the non-defaulting members’ clearing/participant funds; the subsidiaries may also require non-defaulting members to contribute additional resources to their clearing/participant funds (assessment powers).” So if you were wondering how they pay up, that’s how. There is no insurance in the traditional sense; all the assets under management are up for collateral for the DTCC to close out a defaulting-member’s (the clearinghouses’) defaults. 50T is the number thrown around because the AUM in 2019 was $50,984,207,000
Straight from their own webpage, “DTC [subsidiary of DTCC] brings efficiency to the securities industry by retaining custody of more than 1.3 million active securities issues valued at US$54.2 trillion as of 7/31/2017, including securities issued in the US and more than 131 countries and territories” (https://www.dtcc.com/about/businesses-and-subsidiaries/dtc). Too flimsy for my tastes though, gonna edit and update again if I can find an actual statement.
For the sake of this argument, well say it's just the 50t