MetLife Inc. is taking a majority stake in a 43-story office tower being built next to San Francisco’s Transbay Transit Center, expanding the biggest U.S. life insurer’s holdings in one of the country’s most expensive office markets.

MetLife formed a joint venture with Chicago-based John Buck Co. and Golub & Co. for the property, called Park Tower at Transbay, the companies said in a statement before the building’s groundbreaking Tuesday. The tower, which doesn’t yet have a tenant, is scheduled for completion in 2018.

Financial terms of the venture weren’t disclosed. Fred Pieretti, a spokesman for MetLife, said the company will own a majority interest in the building.