Bonds . . . treasury bonds. They are still considered the safest investment on the planet.

"The U.S. has benefitted because other countries needed dollars as reserves and for transactions. No other market has near the depth and liquidity of the U.S. financial system, the linchpin of which is the Treasury market. Not even the loss of America's triple-A rating by Standard & Poor's reduced the attraction of U.S. government obligations."
Will China's Sale of Treasuries Force the Fed to Buy? - Barron's