It's very detailed. These things are very voluminous. The explanatory notes for all the departments amount to a stack a couple of metres high, if you put them all together. The senators focus on the things they're interested in. There will be elaborate explanations of programs that don't attract any attention, simply because people are pretty familiar with them, they understand what they're about, and they're not the focus of attention. They are presented every year, nonetheless, in great detail.
Senators arrive, they go through the explanatory notes and the things they're interested in, and they ask detailed questions. They're able to get down to hundred-dollar amounts, if they really want to. It's a matter of their focusing on the things they're interested in. The departments also expand their explanations of things that they know, from past experience, senators are interested in. If they have a program they know senators are particularly interested in, they expand their explanation of that program.