Every quarter, large money-managers have to disclose what they've bought and sold via 13F filings. While Fools don't always (or even usually) follow what the big money does, we can often glean an idea or two by tracing their footsteps.

A look at Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) most recent 13F, or Warren Buffett's annual shareholder letter, could easily make it seem like U.S. Bancorp (NYSE:USB) -- in which Berkshire bought another 705,000 shares in the first quarter -- is Buffett's second-most favorite bank behind Wells Fargo, Berkshire's largest stock holding. However, this overlooks one major detail about another huge bank investment that doesn't show up on the 13F: Berkshire's $5 billion warrants in Bank of America (NYSE:BAC)

In the video below, Foolish contributor Jason Hall gives some insight into why these huge banks are such a big part of the Berkshire Portfolio. Do they belong in yours? That depends. Check out the video for more insight.