The high-flying shares of Lincoln Financial Group., the Radnor-based life insurer and annuities company, were down slightly in Friday trading after Lincoln said it was acquiring Liberty Mutual Insurance Group of Boston's group benefits business.

The combined business — representing Lincoln's biggest deal in over a decade — will rank among the largest in the U.S. group-benefits market, with around 7 percent of combined U.S. employee life, dental, vision, critical illness and accident policies, and 14 percent of disability insurance, the company said.

Lincoln has been looking to grow its own benefits business through an acquisition — and buying the less-profitable Liberty business will nearly double Lincoln's employee-group insurance premiums to around $3.7 billion a year, Richard L. Mucci, the Lincoln executive who will head the combined business, told investors in a conference call.

Under chief executive Dennis R. Glass, Lincoln has lately sought to diversify its business. Analysts estimate the company will report after-tax income of around $1.6 billion when it posts full-year 2017 results, on sales of more than $14 billion, both record highs, according to analysts polled by Bloomberg LP.

As part of the deal, Lincoln, whose shares Friday closed at a record high of $84.37, will transfer life and annuity assets from the Liberty business to Dai-Ichhi 's Protective Life Insurance Co. unit through a reinsurance arrangement. That left the net purchase price to Lincoln around $1.02 billion, which Lincoln said it would finance partly through borrowing.

Lincoln is relying on a total of $100 million in expense cuts to make the deal profitable, noted Suneeth Kamath, an insurance stock analyst for Citigroup, during an investor conference call with Lincoln's bosses.

Lincoln officials said the savings would come from consolidating the companies' software systems on a single platform, and shutting back offices. Lincoln currently employs around 9,000. The Liberty deal is Lincoln's biggest since its 2005 acquisition of North Carolina-based Jefferson-Pilot Corp.

The company also plans to boost rates for current group customers by about 5 percent, Lincoln executives said. Liberty's group insurance business mostly targets employers with more than 5,000 workers; Lincoln has focused on firms with under 1,000.

While Liberty's recent group profit margins have been weak, around 1 percent, that's just "a temporary dip," Lincoln chief executive Dennis R. Glass told analysts.

He said Liberty sells "best-in-class" disability insurance, "focused on [worker] recovery and return to work." Lincoln's own group business has had a profit margin of around 5 percent. Glass said the combined company will eventually have margins above that level.

Liberty is selling the business to focus on property and casualty insurance, chief executive David H. Long said in a statement.