How to apply a header level discount percent that translates to all order lines

Requirement:

Apply a discount defined at the header of an order that is translated down to each line.

Solution:

A percent-based discount needs to be applied to all lines on an order. This cannot be done manually for orders with an extensive number of lines. Need the ability to define the discount percentage somewhere on the header level so it is displayed across all lines on the order. Every line will take the discount.