The fund normally invests at least 80% of its net assets plus any borrowing for investment purposes in a diversified portfolio of bonds, including corporate bonds of domestic issuers and of foreign issuers payable in U.S. dollars, short-term debt instruments, mortgage- and asset-backed securities, bonds of foreign government issuers (including its agencies and instrumentalities) payable in U.S. dollars, and U.S. Treasury securities and other debt securities issued or guaranteed by the U.S. government (including its agencies and instrumentalities).