Author: Adam Levy, The Motley Fool

He added $13.8 billion last quarter.

He’s relied on it since the 1980s, and now more than ever.

Here is what’s going on, and several simple ways to invest.

While two of them trade for exceptionally low valuations, the other could still be a better buy.

They’re currently trading at attractive valuations, and Buffett’s taking advantage while he can.