Comment by guffaw5

Banks have a ton of cash, and they're worried about inflation. So, they store their cash with the fed (through a repo [repurchase] agreement) temporarily.

[0] What is a repo? - https://www.richmondfed.org/publications/research/econ_focus...

[1] Repos in charts - https://fred.stlouisfed.org/series/RRPONTSYD