It’s not really $21T in cash but rather $21T worth of book-cooking “adjustments” to make the numbers align. This article gives a good overview: https://www.nytimes.com/2018/12/03/us/politics/fact-check-pe...

The NYT article claims that’s the absolute value of cooked assets and liabilities rather than the net amount but in truth it’s misappropriation so many levels deep (and recursive in parts) that you can’t even tell whether dollars are being made or lost. Purposely, I can only presume.