Answer:
The CIA estimated that 3.9% was used in 2005. They further estimated that the total GDP was $1,465,000,000,000 in 2010 adjusted for the exchange rate.
Obviously using estimated numbers for different years will yield, at best, a questionable amount, but those were the numbers I found. They indicate an annual expenditure of, very roughly, $57,135,000,000.
See the related link.