NISA Investment Advisors' Pension Surplus Risk index fell to 8.6% in June, a 90-basis-point drop from May.
NISA said June's index level marked an historical low for the index, which aims to be a forward-looking estimate of funded status volatility for U.S. pension plans. Its previous low point was reached in March and April 2013 when the index fell to 8.9%.
Both interest rate volatility and return-seeking asset volatility fell in June.
Annualized volatility for the liability component fell 100 basis points, to 6.4%, while asset volatility fell to 7.2% from 7.5% in May.