paper trail

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A series of documents providing evidence of one's actions.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic A written record, history, or collection of evidence.
• noun idiomatic the records left by a person or organization in the course of activities.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the written evidence of someone's activities