That number was closing in on two billion at Knight Capital alone.
The number was $1,821,957,000 in 2016.
It's filed under the Liabilities section and entitled:
Fair value probably means something close to .17¢ per share today. Of course, if the share price went up really quickly, the fair value would likely be much higher.
So what exactly are "Financial instruments sold, not yet purchased, at fair value"? They are: