The Treasury Department said Monday that Saudi Arabia held $116.8 billion in U.S. debt at the end of March, revealing for the first time the holdings of the world's biggest oil exporter. The pile puts Saudi Arabia among the largest foreign nation holders of American debt. Still, it sits well behind countries like China and Japan, which both had more than $1 trillion in Treasury securities at the end of March. Saudi Arabia's holdings could be even larger than officially listed, according to Bloomberg, which first reported the total. Saudi Arabia has about $587 billion in foreign reserves and central...