In laymans terms you need to create an new Excel Workbook then use a recordset that is grouped by customer
You would start by enumerating throught the recordset by creating a new recordset that is based on the current customer.
Use the CopyFromRecordset Rst method to copy to the current worksheet
Then every time the recorset encounters a new customer you add an new worksheet to the workbook and make this the active workbook and repeat.
Code:
Create Excel Workbook Instance
Rs1 = CurrentDb.OpenRecordset("QryGroupedBycustomerId")
Do While Rs1.EOF
Rs2 = CurrentDb.OpenRecordset("Select * From Query Where CustId=" & Rs1("CustId"))
.WorkSheets.Add(Rs1("CustId"))
.Range("A1").CopyFromRecordset Rs2
Rs1.MoveNext
Loop
Close Recordsets
Close and Quit Excel
As you can see this is aircode and is untested and used for brevity.
David