Wells Fargo & Co.'s chief financial officer, Howard Atkins, has resigned for personal reasons, the bank announced late Tuesday.

He was immediately succeeded by Wells' chief administrative officer, Timothy Sloan.

"We understand Howard's decision to retire after having served Wells Fargo successfully for nearly ten years and after having had a financial services career that has spanned four decades," Chief Executive Officer John Stumpf said in a press release.

According to a simultaneously filed notice with the SEC, "Mr. Atkins will be on a personal unpaid leave of absence until his retirement from the Company on August 6, 2011."

Oscar Suris, Wells' head of communications, said the company did not intend to discuss Atkins' departure beyond the press release. Neither Sloan or Atkins was available to comment.

Paul Miller, a managing director of FBR Capital Markets, praised the departing CFO for "consistent" reporting and management. The speed of the departure struck him as notable.

"Howard Atkins was well trusted and well liked by the Street," Miller said. "He's leaving abruptly, and you're bringing in an unknown to take his job."

While he has kept a low profile, Sloan has been with Wells for 23 years. Promoted to the newly created chief administrative officer job just last September, he previously headed up Wells' commercial banking operations.

Wells' announcement contained no information about Atkins' future plans. He has worked for Wells since 2001, previously serving as the CFO for New York Life Insurance Co. and Midatlantic Corp.