in name only
Also, only in name. Nominally, not actually. For example, He's the chief executive in name only; his vice-president makes all the decisions, or Theirs was a marriage only in name; they lived on different continents. [Late 1300s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.