I'm not entirely certain what you are asking here.
You have two details sections, A and B. They might look like:
Originally posted by Details A
{SomeData1}
{SomeData2}
{SomeData3}
Originally posted by Details B
__________________________
{OtherData1}
{OtherData2}
{OtherData3}
Yes?
Now, there are several possible scenarios:
A and B are on the same page entirely. Print the separator line.
A spans a page break. Print the separator line?
B spans a page break. Print the separator line?
A page break comes exactly between A and B. Suppress the separator line.
How does that look? Is that more or less what you're trying to achieve?