The game will replace all currency denominations with smaller ones if inflation starts to get too high, so I would guess it's that. It pops-up a special news dialog, when the government does that.

Hello,

I was wondering if the game automatically corrects numbers when they get to big. As I was playing just now, I reached about 4.5 trillion in equity and suddenly all monetary values in the game (revenue, profit, expenses, assets, market cap etc...) got divided by 100 and my annual profit of 20 billion got cut down to 200 million.

Is this a bug or is it meant to happen?