Be patient with my ignorance. Are FCM futures brokers? So, if customers default, FCM got to pay up? Is Interactive Brokers considered a FCM? IBKR was not mentioned in the report. I guess IBKR was saved by their auto-liquidation algo.
https://www.investopedia.com/terms/f/fcm.asp https://en.wikipedia.org/wiki/Commodity_broker http://www.cftc.gov/MarketReports/financialfcmdata/index.htm