It's not Buffett and team buying stock, but instead U.S. Bancorp's (NYSE:USB) share repurchases have trimmed the float enough to push Berkshire Hathaway's (BRK.A, BRK.B) stake above 10%.
Berkshire Hathaway is the bank's top shareholder with 150M shares, and Warren Buffett’s direct ownership totals 884K shares.

