Average renewal premium rates for insurance and facultative reinsurance increased 11.3% in 2020 and 4.8% in 2019, when adjusted for changes in exposures. Average renewal premium rates for insurance and facultative reinsurance excluding workers' compensation increased 13.6% in 2020 and 6.9% in 2019, when adjusted for changes in exposures. • Insurance gross premiums increased 6% to $7,837 million in 2020 from $7,398 million in 2019. Gross premiums increased $270 million (11%) for other liability, $196 million (20%) for professional liability, and $92 million (5%) for short-tail lines and $74 million (9%) for commercial auto, and decreased $193 million (15%) for workers' compensation. • Reinsurance & Monoline Excess gross premiums increased 17% to $1,010 million in 2020 from $864 million in 2019. Gross premiums written increased $105 million (22%) for casualty lines, $27 million (14%) for property lines, and $14 million (7%) for monoline excess. A summary of gross premiums written in 2020 compared with 2019 by line of business within each business segment follows: Net premiums written were $7,262 million in 2020, an increase of 6% from $6,863 million in 2019. Ceded reinsurance premiums as a percentage of gross written premiums were 18% in 2020 and 17% in 2019. Premiums earned increased 4% to $6,931 million in 2020 from $6,633 million in 2019. Insurance premiums (including the impact of rate changes) are generally earned evenly over the policy term, and accordingly recent rate increases will be earned over the upcoming quarters. Premiums earned in 2020 are related to business written during both 2020 and 2019. Audit premiums were $128 million in 2020 compared with $199 million in 2019. Net Investment Income. Following is a summary of net investment income for the years ended December 31, 2020 and 2019: Net investment income decreased 10% to $584 million in 2020 from $646 million in 2019 primarily due to a $92 million decrease in income from fixed maturity securities driven by lower investment yields and repositioning a larger portion of the investment portfolio to cash and cash equivalents, a $15 million decrease in income from investment funds and an increase in investment expenses of $3 million, partially offset by a $43 million increase in arbitrage trading account and a $5 million increase in equity securities. Investment funds are reported on a one quarter lag. The average annualized yield for fixed maturity securities was 2.7% in 2020 and 3.4% in 2019. The effective duration of the fixed maturity portfolio was 2.4 years at December 31, 2020 and 2.8 years at December 31, 2019. The Company shortened the duration of its fixed maturity security portfolio, thereby reducing the potential impact of mark-to-market on the portfolio and positioning the Company to react quickly to changes in the current interest rate environment. Average invested assets, at cost (including cash and cash equivalents), were $20.0 billion in 2020 and $19.1 billion in 2019. Insurance Service Fees. The Company earns fees from an insurance distribution business, a third-party administrator, and as a servicing carrier of workers' compensation assigned risk plans for certain states. Insurance service fees were $89 million in 2020 and $93 million in 2019. The decrease was primarily due to a reduction of assigned risk plan business. Net Realized and Unrealized Gains on Investments. The Company buys and sells securities and other investment assets on a regular basis in order to maximize its total return on investments. Decisions to sell securities and other investment assets are based on management’s view of the underlying fundamentals of specific investments as well as management’s expectations regarding interest rates, credit spreads, currency values and general economic conditions. Net realized and unrealized gains on investments were $74 million in 2020 compared with $121 million in 2019. In 2020, the gains reflected net realized gains on investment of $99 million, including the sale of a building for a gain of $105 million, and decreased by a change in unrealized 45 Amount Average Annualized Yield (In thousands) 2020 2019 2020 2019 Fixed maturity securities, including cash and cash equivalents and loans receivable $ 426,563  $ 517,925  2.7  % 3.4  % Investment funds 54,253  69,194  4.5  5.2  Arbitrage trading account 77,931  34,585  14.6  7.8  Real estate 24,027  24,218  1.2  1.2  Equity securities 10,172  5,439  2.7  2.0  Gross investment income 592,946  651,361  3.0  3.4  Investment expenses (9,125) (5,747) —  —  Total $ 583,821  $ 645,614  2.9  % 3.4  %