Bertolini testified on Monday that Aetna's initial estimate was that the merger would create $1.25 billion in efficiencies. He said that estimate had since been raised to $3 billion, because of combined technology systems, some potential layoffs and other strategies.
He also said he had "very high confidence that we will deliver on those numbers."
But Conrath noted that a 2013 merger with Coventry remained incomplete and some Coventry computer systems remained outside the Aetna network.
He also said Aetna's estimates of the cost of the transaction, beyond the purchase price, would eat a chunk of the efficiencies. Aetna estimated that the cost of implementing the deal at $1.5 billion.
This article was provided by Reuters.