Correct usage of USD

I am currently writing an essay, I have to state there is a $1 million prize for something. What is the correct way of stating this amount?

I have gone with "one million USD", do you think this is acceptable or is there a preferred format?

If you and your essay readers are in the U.S., then they will correctly infer one million U.S. dollars from $1 million.

Currency abbreviations (such as USD, CHF, CAD, JPY, and EUR) are used by currency traders to denote currency pairs.

I would avoid USD unless your essay readers might confuse the prize for Canadian or Australian dollars. In those cases, you might write it as

a $1 million (CAD) prize

the fabulous $1 million (AUD) prize

I would only use an abbreviation like "USD" in a context where other such abbreviations are used or at least would seem appropriate. If you're writing general text, with all the other words spelled out normally, it would be odd to suddenly use an abbreviation here.

Also, I think most general readers would not realize what "USD" stands for without some context. I mean, if you just said, "the prize is one million USD", unless you have been talking about multiple foreign currencies in this context before this, I don't think most readers would instantly realize what that stands for.

If you were writing to an American audience, who would normally expect all dollar amounts to be American dollars unless otherwise specified, you should simply say "$1 million". I'm not sure what conventions are in other countries, but as an American, if I was writing for an American audience and the prize was in, say, Australian dollars, I would write "$1 million (Australian)" or "one million Australian dollars".

I'd avoid "$1 million (USD)" or "one million dollars (USD)" because it's redundant: that spells out to "one million dollars (United States dollars)", and grates like "ATM machine", etc.

If you are writing an article for bankers or international financiers, that's different, then it's conventional to write "US$1 million", etc. and they know what you mean.

To be honest I believe we should be moving to international accepted norms for currency reporting, namely ISO 4217. In this case, one would use USD. In Europe they have clearly defined standards for reporting currency in documents. In this case they use the ISO 4217 code of EUR, see (http://publications.europa.eu/code/en/en-370303.htm).

The Economist Magazine is a common example of bad reporting in both currency abbreviations(often ambiguous) and use of SI units (i.e m (metre) for million rather than M for million).