Hola Adriano
How you document depends a lot on how many firewalls you are managing. If it's just a few firewalls, a spreadsheet is probably good enough. You should find a way to keep different versions, so if you make a change, you can see the difference. If you're handy with linux, you can write some scripts to read the access lists and keep multiple versions.
If you have a lot of firewalls, then I suggest you look at products like Cisco security manager or Solsoft policy manager. they will allow you to create policies and push them to multiple firewalls at once. they have reporting tools so you can keep track of the various policies.
Ron