[nradov]

In banking terms, the main assets are the outstanding loans. Fractional reserves (deposits as a percentage of loan balances) are no longer very relevant to modern banking. The limit in the USA was cut to zero in 2020.

https://www.federalreserve.gov/monetarypolicy/reservereq.htm

The focus is now more on capital for assessing bank health.

[FabHK]

Just to add, what's called "capital" in banking is basically the bank's equity. And there are proposals to force banks to carry a lot more equity (even if, my god, that reduces the return on equity earned - with a concomitant reduction in risk, though, thus making the equity no less valuable, theoretically speaking).

See for example The Bankers' New Clothes: What's Wrong with Banking and What to Do about It (2014) by Anat Admati and Martin Hellwig.