Skadden, Arps, Slate, Meagher & Flom won membership in the most exclusive kind of club in December—the kind with just one member.

The firm is advising E.I. du Pont de Nemours & Co. in its planned merger with Dow Chemical Co. The all-stock deal will yield a combined entity valued at a whopping $130 billion, making Skadden the first legal adviser to handle more than $1 trillion in announced M&A deals in a single year.