In regards to Line Item Detail, you can use the spreading method to look at Actuals as a driver - more specifically you can use previous year actuals in the spread area for budgeting. Please note, however, that it can get messy as you have to offset the months because most likely you will be doing budgeting in October when you do not have actuals for periods 10,11, and 12.
Instead of even, you would point it to one of the previous years in the dropdown. From there you can offset if needed with the offset choice - you may have to set up comparison.
It's automatic if you bring a value into comparable data - it will not have the option without dragging in a measure as it will not know what to compare it to: