Sullivan & Cromwell is seeing double on the billion-dollar deal front this week.

Following a judge's ruling that Kirkland & Ellis should not move forward on representing Teva Pharmaceutical Industries Ltd. in its $40 billion unsolicited bid for Mylan NV, Sullivan & Cromwell was beckoned by the would-be acquirer to step in for its previous counsel. The switch-up—which stems Kirkland's prior work for various Mylan entities, potentially giving the firm access to confidential company information—will see Kirkland object to the potential change.

For its part, Sullivan & Cromwell also secured work on behalf of Japanese insurance company Tokio Marine Holdings Inc. on its $7.5 billion buy of Houston-based HCC Insurance Holdings Inc. Willkie Farr & Gallagher is advising HCC in the deal, while Debevoise & Plimpton and Skadden, Arps, Slate, Meagher & Flom are counseling Evercore Partners and Credit Suisse, respectively, as financial advisers to Tokio, according to sibling publication The Asian Lawyer.