April 9 (Bloomberg) — Standard & Poor's says the California Public Employees Retirement System can't blame it for almost $800 million in losses on top-rated investments that later collapsed because its assessments are opinions and not guarantees or facts.

McGraw Hill Financial Inc.'s S&P unit and Moody's Investors Service Inc. accuse Calpers, the largest U.S. pension fund, of trying to shift responsibility for the losses that occurred after it outsourced investment decisions to money managers who put $1.3 billion into three investment vehicles backed by subprime mortgages in 2006 and 2007.

The investments, made without the fund's knowledge, crumbled amid the housing crisis, according to court filings. Calpers sued the ratings companies in 2009 and a California judge ruled in 2012 that S&P and Moody's must face claims they made negligent misrepresentations.