Check the Newspaper! you get detailed reports of what happened with hours and stuff.
Thing is though that when you attack an AI they instantly send troops from other provinces to defend the one you are attacking. When you were away that is most likely what happened. I think your troops defeated the original AI stack that was there which is why their losses where not displayed correctly.
As for being idle, your infantry has both attack and defense stats. When someone attacks your infantry/stack and they are idle they will only use defensive damage. You can instruct them to attack and you should see the cooldown of their attack.
This is how its supposed to work btw. For example: if you have a stack of troops with Armoured Cars in them you want to keep them idle and not attack the enemy. While idle your Armoured Cars will only use defensive stats, which is 2x more than their attack. If you instruct them to attack however, you will see that your Armoured Cars will get destroyed faster and deal less damage.