Item 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Our earnings and financial position are exposed to financial market risk, including those resulting from changes in interest rates.

The level of our pretax earnings is subject to market risk due to changes in interest rates and the resulting impact on investment income and interest expense. In the past we have, and in the future we may enter into interest rate swap agreements depending on market conditions and other factors. Amounts borrowed under the revolving credit portion of our $2.0 billion unsecured revolving credit agreement bear interest at either LIBOR plus a spread or the base rate plus a spread. There were no borrowings outstanding under our credit agreement at December 31, 2018 or December 31, 2017.

Interest rate risk also represents a market risk factor affecting our consolidated financial position due to our significant investment portfolio, consisting primarily of fixed maturity securities of investment-grade quality with a weighted average S&P credit rating of AA at December 31, 2018. Our net unrealized position decreased $402 million from a net unrealized gain position of $198 million at December 31, 2017 to a net unrealized loss position of $204 million at December 31, 2018. At December 31, 2018, we had gross unrealized losses of $213 million on our investment portfolio primarily due to an increase in market interest rates since the time the securities were purchased. There were no material other-than-temporary impairments during 2018. While we believe that these impairments are temporary and we currently do not have the intent to sell such securities, given the current market conditions and the significant judgments involved, there is a continuing risk that future declines in fair value may occur and material realized losses from sales or other-than-temporary impairments may be recorded in future periods.

Duration is the time-weighted average of the present value of the bond portfolio’s cash flow. Duration is indicative of the relationship between changes in fair value and changes in interest rates, providing a general indication of the sensitivity of the fair values of our fixed maturity securities to changes in interest rates. However, actual fair values may differ significantly from estimates based on duration. The average duration of our investment portfolio, including cash and cash equivalents, was approximately 2.9 years as of December 31, 2018 and 4.1 years as of December 31, 2017. Based on the duration including cash equivalents, a 1% increase in interest rates would generally decrease the fair value of our securities by approximately $365 million.

We have also evaluated the impact on our investment income and interest expense resulting from a hypothetical change in interest rates of 100, 200, and 300 basis points over the next twelve-month period, as reflected in the following table. The evaluation was based on our investment portfolio and our outstanding indebtedness at December 31, 2018 and 2017. Our investment portfolio consists of cash, cash equivalents, and investment securities. The modeling technique used to calculate the pro forma net change in pretax earnings considered the cash flows related to fixed income investments and debt, which are subject to interest rate changes during a prospective twelve-month period. This evaluation measures parallel shifts in interest rates and may not account for certain unpredictable events that may affect interest income, including unexpected changes of cash flows into and out of the portfolio, changes in the asset allocation, including shifts between taxable and tax-exempt securities, and spread changes specific to various investment categories. In the past ten years, changes in 3 month LIBOR rates during the year have not exceeded 300 basis points, have not changed between 200 and 300 basis points, have changed between 100 and 200 basis points twice, and have changed by less than 100 basis points eight times.