Property-casualty insurer Travelers Cos. posted a 20% decline in net income in the third quarter, weighed down by storm damage and car-wreck related claims.

Travelers is among the largest issuers of insurance to U.S. businesses, and it sells car and home insurance to individuals and families.

Analysts’ estimates of Hurricane Ida’s late summer...

Property-casualty insurer Travelers Cos. posted a 20% decline in net income in the third quarter, weighed down by storm damage and car-wreck related claims.

Travelers is among the largest issuers of insurance to U.S. businesses, and it sells car and home insurance to individuals and families.

Analysts’ estimates of Hurricane Ida’s late summer industrywide damage hovers around $30 billion. Travelers said its third-quarter catastrophe losses totaled $501 million pretax, compared with $397 million in pretax losses a year earlier. This year’s losses were primarily from Ida but also severe storms in several regions of the U.S.

The company, part of the Dow Jones Industrial Average, reported a net income of $662 million, a decline from $827 million in the prior-year quarter. Last year, Travelers’ third-quarter catastrophe costs were offset as the company booked a recovery from utility PG&E Corp. of $403 million on a pretax basis, related to California wildfires in 2017 and 2018.

As one of the first big property-casualty insurers to report quarterly earnings, Travelers’ results are watched closely as a bellwether for others. Its shares were up about 3%.

The company’s personal-insurance unit, which combines results for car and home insurance, posted a loss of $2 million, down from income of $392 million in the year-earlier period.

In the year-earlier period, Travelers was one of many U.S. car insurers to get a lift from business shutdowns and work-from-home arrangements that led to a drop in miles driven and a sharp reduction in traffic crashes.

As of this year’s second quarter, car insurers began facing tougher comparisons with the year before as drivers were returning to the nation’s roads again in large numbers.

Analysts have forecast increasing crash frequency throughout 2021, with insurers’ key profitability metrics expected to be weaker as a result.

The company said it recorded net written premiums, a closely watched measure of revenue, of $8.32 billion, up 7% compared with the prior-year quarter, with growth in all its key segments. Its big business-insurance segment benefited from strong renewal rate increases, it said.

Travelers Chairman and Chief Executive Alan Schnitzer called the earnings “a strong result despite significant catastrophe losses during the quarter.”

In the year-earlier period, property insurers were hit by wildfires in western states, Tropical Storm Isaias, Hurricane Laura and a powerful storm—known as a “derecho”—that tore across the Midwest contributed to the catastrophe losses, the company said.

Earlier

From New York City to Louisiana, residents in areas pummeled by Hurricane Ida and its remnants surveyed damage to their properties in early September. Most home policies don’t include flood coverage and President Biden asked insurance companies to not deny assistance to those who were forced to evacuate. Photo: Adrees Latif/Reuters The Wall Street Journal Interactive Edition

Travelers said its segment income for business insurance was $558 million, an increase of $193 million. Among unfavorable developments, the company added $225 million to its asbestos reserves, in what has been a decadeslong, industrywide effort to pay claims on old policies.

In general, business insurers’ results have been better than expected in the face of the Covid-19 pandemic. Last year, analysts were concerned that they would be hurt by adverse judicial rulings as restaurants, retailers and many other businesses seek payouts under business-interruption provisions for income lost during government-ordered shutdowns.

Insurers maintain the coverage is aimed for disruptions following fires and other events that damage property and that many policies specifically exclude virus-related claims. Of rulings so far, insurers have overwhelmingly prevailed.

Write to Leslie Scism at leslie.scism@wsj.com