United Airlines, on the hunt for a megadeal, last year approached Delta Air Lines about a merger that would have combined the two most valuable U.S. carriers, according to people familiar with the matter. As part of the pitch, United Chief Executive Scott Kirby made a call to Delta CEO Ed Bastian, some of the people said.

Delta leaders discussed the approach and merits of a potential deal as part of preliminary due diligence, people familiar with the matter said. The talks didn't progress and both companies later moved on from the proposal, they said.

The outreach, which hasn't previously been reported, underscores Kirby's appetite for taking big swings in pursuit of his global ambitions for United. His later attempt to engage in merger talks with American Airlines, which American rebuffed, also became public earlier this year.