(Sharecast News) - American insurance giant AIG on Thursday announced the sale of a 20% stake in retirement and insurance firm Corebridge Financial to Japanese peer Nippon Life for $3.8bn.

AIG disposed of 120m shares at $31.47 a piece, a premium to Corebridge's closing price of $30.16 on Wednesday.

Corebridge shares were up 12% at $33.70 by 1108 in New York, taking its year-to-date rise to 53%. AIG was gaining nearly 1% to $79.50.

The sale leaves AIG with a 9.9% shareholding, a level which it has agreed to maintain for two years after the deal completes, according to the terms of the transaction.

"Nippon Life is well known in the financial services industry for its leadership in the Japanese insurance market and is globally recognised for its strong performance and corporate reputation," said AIG's chair and chief executive Peter Zaffino.

"We are pleased to have Nippon Life become a strategic partner to Corebridge and believe that they will add meaningful value as an investor," he said.