Where it is
Open My bookings and then the booking itself. Its own page carries a panel headed Receipt, alongside the flights and the contact details given at checkout.
What it shows
The fare, the taxes and fees, and the total, each in the currency the booking was made in — with the currency's own code printed beside the total so there is no guessing which dollar it means. Below that, the card: its scheme and its last four digits, which is all of a card this site ever keeps.
A cancelled booking still shows its receipt. The total is labelled differently there, because what it records is what the booking was for rather than something still owing.
What it is not
It is not an invoice and not a tax document. There is no VAT breakdown, no supplier details and no invoice number, because there was no sale — nothing was charged, so there is nothing to account for. See Paying for a booking.
If you came here looking for something to give to an accounts department, this is not it, and no version of this site can produce one.
It reads in its original currency
The figures do not follow the currency switcher. A booking keeps the currency it was made in and the rate that applied at the time, so a receipt read months later says what it said on the day — see Prices and currencies.
For as long as the session lasts
The receipt is part of the booking, and the booking is only listed while the browsing session that made it is alive. Close the browser and there is no page to open — see Ticket did not arrive.