(Reuters) - American International Group ( AIG ) sailed past Wall Street estimates for third-quarter profit on Monday as the insurer benefited from strong underwriting and higher returns on investments.

General insurance net premiums written, on a comparable basis excluding the impact of divestitures, climbed 6% in the quarter to $6.38 billion.

AIG's general insurance accident year combined ratio came in at 88.3% on an adjusted basis, compared with 86.9%, a year earlier. A ratio below 100 signifies that the insurer earned more from premiums than it paid out in claims.

The insurance industry is largely immune to economic vagaries, since most of its policies are either bought by employers for their workers or mandated by governments.

A booming stock market has also helped insurers book high returns on their investments.

Net investment income rose 14% to $973 million in the third quarter, driven by dividends received from Corebridge and higher income from alternative investments and equity and fixed-maturity securities.

AIG retains a stake in Corebridge, the life and retirement insurer it spun off in 2022.

The gains in underwriting and investment income helped offset higher catastrophe losses.

Insurers have faced billions in payouts in recent years as climate-related disasters intensify. The 2024 U.S. hurricane season has been especially destructive, with major storms impacting multiple states.

AIG posted catastrophe losses of $417 million in the quarter, of which $324 million was in North America, with losses predominantly from windstorms and hailstorms.

"In a challenging catastrophe environment, this performance is remarkable, with industry insured losses expected to top the 2023 total of $125 billion," CEO Peter Zaffino said.

AIG - one of the world's largest commercial insurers - reported adjusted after-tax income attributable to common shareholders of $1.23 per share in the three months ended Sept. 30, from $1.04 a year earlier.

Analysts on average had expected $1.10 per share, according to estimates compiled by LSEG.

(Reporting by Manya Saini in Bengaluru; Editing by Anil D'Silva)