JPMorgan Chase & Co. Chief Executive Officer Jamie Dimon plans to sell shares currently worth about $141 million, the first such transaction since he took the helm at the Wall Street giant almost 18 years ago.

Starting next year, Dimon and his family will dispose of 1 million of the lender’s shares for financial diversification and tax-planning purposes, according to a regulatory filing Friday. JPMorgan shares closed at $140.76 in New York on Thursday.

Dimon “continues to believe the company’s prospects are very strong and his stake in the company will remain very significant,” JPMorgan said in the statement. The planned transaction, which is subject to the terms of the bank’s stock-trading plan, would be the CEO’s “first such stock sale during his tenure at the company.”

The increase of almost 250% in JPMorgan’s shares during Dimon’s tenure — more than 10 times the gain in the S&P 500 Financials Index — has helped turn the executive into a billionaire. In early 2009, Dimon bought 500,000 shares in the bank as a sign of confidence amid a stock slump. He made an identical move in 2016, spending about $38 million on the two rounds of purchases.