Warren Buffett's Berkshire Hathaway Inc. said on Friday it had cut its Wells Fargo & Co. stake to 3.3%, further reducing what had once been a $32 billion investment in the bank.

Berkshire said in a regulatory filing it owned about 137.6 million shares, worth $3.4 billion, of the fourth-largest U.S. bank by assets, down about 100 million from the end of June.

Buffett began investing in Wells Fargo (WFC) in 1989, but has been reducing Berkshire's stake as the bank struggles to recover from a series of scandals over its treatment of customers, including the opening of accounts without their knowledge.

Wells Fargo's ability to grow remains subject to a Federal Reserve limit. Moody's Investors Service on Wednesday lowered its rating outlook on the bank to "negative" from "stable," citing the bank's slower-than-expected ability to resolve governance and oversight issues from previous years.

Berkshire still owns shares of several other banks, including Bank of America Corp, which became its largest common stock holding other than iPhone-maker Apple Inc.

Buffett's conglomerate also owns dozens of operating businesses including the BNSF railroad and Geico auto insurer.