U.S. investment-grade fixed income outpaced high yield by 135 basis points through the first eight months of 2014. The S&P U.S. Issued Investment Grade Corporate Bond index was up 7.05% through August, compared to 5.7% for the S&P U.S. Issued High Yield Corporate Bond index.

AAA-rated bonds returned 8.01% through August.

S&P said in a news release that holding the 10-year U.S. Treasury alone has returned 8.42% year-to-date, as the yield has dropped to 2.33% at the end of August from 3.03% at the end of 2013.