How detailed is the estimate you show your customers?

Question

For custom software, when you are giving your customer an estimate, how much detail do you tend to include?

Do you:

• break it down into small tasks that can be done in a few hours and give them the full list?
• give them one big number and work towards that? And if so does that come from a more detailed estimate that you don't need to show them?
• Do you break it up into big "phases" and give them a number of hours for each phase?

This isn't for fixed bid contracts or anything, just more of a "We think this will cost you X hours at $Y an hour" kind of situation.