Table of Contents Duration A primary objective in the management of the investment portfolio is to optimize return relative to the corresponding liabilities and respective liquidity needs. Our views on the current interest rate environment, tax regulations, asset class valuations, specific security issuer and broader industry segment conditions as well as domestic and global economic conditions, are some of the factors that enter into an investment decision. We also continually monitor exposure to issuers of securities held and broader industry sector exposures and may from time to time adjust such exposures based on our views of a specific issuer or industry sector. A further consideration in the management of the investment portfolio is the characteristics of the corresponding liabilities and the ability to align the duration of the portfolio to those liabilities and to meet future liquidity needs, minimize interest rate risk and maintain a level of income sufficient to support the underlying insurance liabilities. For portfolios where future liability cash flows are determinable and typically long term in nature, we segregate investments for asset/liability management purposes. The segregated investments support the long term care and structured settlement liabilities in the Life & Group segment. The effective durations of fixed income securities and short term investments are presented in the following table. Amounts presented are net of payable and receivable amounts for securities purchased and sold, but not yet settled. December 31 2019 2018 (In millions) Estimated Fair Value Effective Duration (In years) Estimated Fair Value Effective Duration (In years) Investments supporting Life & Group $ 18,015 8.9 $ 16,212 8.4 Other investments 26,813 4.1 25,428 4.4 Total $ 44,828 6.0 $ 41,640 6.0 The investment portfolio is periodically analyzed for changes in duration and related price risk. Certain securities have duration characteristics that are variable based on market interest rates, credit spreads and other factors that may drive variability in the amount and timing of cash flows. Additionally, we periodically review the sensitivity of the portfolio to the level of foreign exchange rates and other factors that contribute to market price changes. A summary of these risks and specific analysis on changes is included in the Quantitative and Qualitative Disclosures About Market Risk included under Item 7A. The carrying value of the components of the Short term investments are presented in the following table. Short Term Investments December 31 (In millions) 2019 2018 Short term investments: Commercial paper $ 1,181 $ 705 U.S. Treasury securities 364 185 Other 316 396 Total short term investments $ 1,861 $ 1,286 44