How to write negative currency in text?

Which version is grammatically correct (given that I hopefully provided at least one correct alternative)?

[...] the company yielded a result to the amount of −€6.680 billion in 2008.

or

[...] the company yielded a result to the amount of €−6.680 billion in 2008.

Since I'm not a native speaker, I'd appreciate any other tips/corrections as well.

In general, you would not write out the minus sign in descriptive text.

The company suffered losses in excess of $7 billion.

The company suffered a 2.4 million dollar deficit.

The words "losses" and "deficit" make the minus sign redundant and unnecessary.

The only example I can think of where you might need to be explicit would be a table, where you might be showing both losses and profits. In that case you would probably use the (loss) syntax common in financial docs:

Company X: $2.1M

Company Y: ($1.4M)

Though you could conceivably use a minus sign as well and your point would be made clear:

Company X: $2.1M

Company Y: -$1.4M

The minus sign is always the leftmost: -(rest of the symbols).

The currency symbol is always adjacent to the figure: €(amount).

To avoid ambiguity and help readability, one may place the minus sign in parentheses:
(-) €6.680