good as one's word, as
Completely trustworthy, dependable, as in The boss said we could leave early on Friday and she was as good as her word. [Second half of 1500s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.