AAA+ sf AAA sf AAA- sf AA+ sf AA sf AA- sf A+ sf A sf A- sf BBB+ sf BBB sf BBB- sf BB+ sf BB sf BB- sf B+ sf B sf B- sf CCC+ sf CCC sf CCC- sf CC+ sf CC sf CC- sf C+ sf C sf C- sf D pi D - AAA+ pi AAA pi AAA- pi AA+ pi AA pi AA- pi A+ pi A pi A- pi BBB+ pi BBB pi BBB- pi BB+ pi BB pi BB- pi B+ pi B pi B- pi CCC+ pi CCC pi CCC- pi CC+ pi CC pi CC- pi C+ pi C pi C- pi AAA+ AAA AAA- AA+ AA AA- A+ A A- BBB+ BBB BBB- BB+ BB BB- B+ B B- CCC+ CCC CCC- CC+ CC CC- C+ C C- 未予评级