It's definitely using COBOL.
Edit:
I should probably explain. The vast majority of digital financial transaction systems in the US were created 60 years ago and run on mainframes. Mainframes are designed to handle billions of simple calculations - but are not very flexible. They have excellent uptime and almost never encounter write errors. When they programmed these mainframes 60/70 years ago they used a state of the art programming language developed by the US DOD known as COBOL. Today it is considered legacy, as it receives no updates. It is not very versatile, but it does simple operations exceprionally well. That also makes it very stable.
As computers developed, IBM also improved mainframes to handle more data, but rewriting a system that "works" into new code that might not work, is expensive and risky. There are also dozens of machines (ATMs) and other systems that are old and that also were written in COBOL. It is highly reliable), so the cost of changing it is simply too great. Because of that COBOL systems have simply been maintained for 60/70 years. It works, it is secure and it does that one thing very well.
A new problem is that very few young programmers know COBOL - it is very much an old man's game.