Fill Down cell in detail line with number in header line until next header line, then use the new number

[vsanthony]

Situation: Customer receipt records, each with a header line with customer ID number and one or more detail lines of items purchased. I want to attach that Customer ID number in the header to each of the detail rows - The number of detail rows is not consistent. The Customer ID is a number, and values in the same column in the detail lines are letters.
Is this possible? If so, I know there's a genius here somewhere who can help me.
I am a low to medium level Excel user - I've written a few simple macros.
Thanks very much!

 

[vsanthony]

Oh duh. I was overcomplicating. I can use a simple IF statement combined with isnumber etc....Thank you.