Insurance conglomerate American International Group Inc. posted strong gains in first-quarter profit from growth in premiums for its global property-casualty business and lower costs from the Covid-19 pandemic.

Net income surged to $3.87 billion, more than doubling net of $1.74 billion in the year-earlier period.

During the quarter, Peter Zaffino took over as chief executive officer from Brian Duperreault, who returned to the company in 2017 in that role to lead a turnaround of the property-casualty unit. Mr. Zaffino was a key lieutenant to Mr. Duperreault in the turnaround.

Long a leading seller of insurance to businesses world-wide, the unit had delivered poor results for years. AIG’s first-quarter earnings release pointed to various measures of improvement, most notably a 69% jump in adjusted pretax income to $845 million, much of it from the international side.

Net premiums written, a key measure of revenue volume, gained 29% in AIG’s North American commercial-lines business, and 20% internationally.