How much of our (american) debt do the Saudis own?

Not just the Saudis; but Kuwait, Qatar, Bahrain, and the UAE? Frequently I read and see about China, Japan, and the UK holding huge amounts of our treasury notes. But since many of the gulf states and Saudi Arabia are some of the wealthiest countries in the world, why wouldn't they be willing to take on some of our debt. I heard about some guy (who knows, Indonesian Prime Minister) who made a point about the Islamic banking system (which I know nothing of) being "better". Just wondering.