How long would it take an advanced computer to crack encrypted data?

I am a writer working on a secret agent story, and I would like to know approximately how long it would take a really good computer (like, government level good) to crack encrypted data. I know that there are all sorts of types of data encryption different encrypters and all that stuff. I don't need to know specifics. I just need to know if it would take a government-level computer a matter of minutes, hours, days, months, etc. to "un-crypt" data. And would it be a different amount of time for different levels of encryption. Any answers would be appreciated! I just want to make my story make sense and not sound ignorant. Thanks!