To reveal or share all the intimate or scandalous details (of something). The aide agreed to tell all about her affair with the senator in an exclusive interview with the news network.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
to tell everything, even the secrets. Some reporter got hold of the actress's maid who offered to tell all for a fee.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.