A.M. Best Co. has assigned a debt rating of “aa-” to Sun Life Financial Inc.’s proposed $600 million senior unsecured fixed/floating rate securities due 2035.

The ratings agency has assigned indicative debt ratings of “aa-” to senior unsecured debt, “a+” to subordinated debt and “a” to preferred shares that can be issued from SLF’s $3 billion shelf registration.

All other ratings remain unchanged. All ratings have a stable outlook.

The proceeds from the senior debt offering will be used for general corporate purposes and will be matched funded.

A.M. Best views Sun Life’s shelf registration as a reasonable means to raise a mix of debt and equity securities over the medium term to fund its general corporate purposes and growth. A.M. Best expects the insurer’s pro-forma debt-to-capital ratio to remain within acceptable levels for the current ratings.

The ratings reflect Sun Life’s diversified and profitable operations, favorable risk-adjusted capitalization and very strong market position in all major business segments in Canada, complemented by growth outside of North America. Moreover, the company enjoys further diversification through its expanding Asia-based operations.

The ratings agency says Sun Life has strong debt servicing capabilities underpinned by its favorable liquidity posture, high quality investment portfolio and continued growth in operating earnings. Sun Life’s earnings are supported by its diverse operations and have been enhanced from expense synergies arising from earlier acquisitions.

Despite overall improved earnings performance, A.M. Best believes Sun Life will remain challenged to significantly improve the operating performance of its U.S. wealth management businesses, where spread compression and volatile equity markets have impacted its fixed annuity and equity-based wealth management businesses.