Dietrich's death was announced Friday by the John A. Freyvogel Funeral Home. It said he died Thursday but did not disclose the cause.
A $265 million gift to Carnegie Mellon, announced Sept. 7, was one of the largest in recent years from an individual to a private university, and the largest in the school's history.
Carnegie Mellon said in a statement Friday that it "will be forever grateful to Bill for his service and philanthropy. Carnegie Mellon and Pittsburgh have lost a great friend."
On Sept. 22, Pitt announced that Dietrich was giving $125 million to Pitt, the single largest gift in that school's history.
Like the gift to Carnegie Mellon, Pitt's gift was set to begin upon Dietrich's death and will be administered by a foundation. In both cases, neither school nor Dietrich disclosed if the gifts were stocks, cash or both.
A Pittsburgh native, Dietrich was born in 1938 and rose to chairman of Dietrich Industries Inc., turning a small family business into the nation's largest manufacturer of light metal construction framing.
A former Marine, Dietrich was an active supporter of business and the arts in western Pennsylvania, serving on the boards of the Allegheny Conference on Community Development, the Pittsburgh Ballet Theatre and the Pittsburgh Symphony Society.
Dietrich had a bachelor's degree from Princeton University and master's and doctoral degrees from Pitt.