Under Payment History in the billing section, you have the option to view two documents for each order.
The order confirmation simply shows how much money was paid for an order and is not meant for accounting purposes. You can view it as soon as an order is made.
If items in the order were refunded, returned, or charged after the order is placed, then the format of the order confirmation will change. You'll see a list of each product in the order with the newly calculated sums below.
An invoice can be used for accounting. It's issued only after an order has been delivered. If an order has multiple shipments, each shipment will have its own invoice.