Which big mismarked derivative was Buffett referring to at the 2016 annual?

[LongHaul]

At this years Berkshire Annual meeting Buffett mentioned a large derivative mismarking.

 

Anyone have any idea which one he was referring to? 

 

“Some of these things get so complicated they’re very hard to evaluate... I know one that’s so mismarked it would blow your mind, and the auditors I don’t think are necessarily capable of holding that behaviour in check,” he said.

 

http://www.telegraph.co.uk/business/2016/05/01/warren-buffett-issues-a-fresh-warning-about-derivatives-timebomb/