What is your basis for believing in the authority of the NT Canon?

Recently I've been in discussion with a friend of mine (Protestant, non-denominational, reformed leanings) about a number of different issues, like predestination and apostolic succession. Through this conversation, I got thinking about the basis for trusting that the right books made it into the NT.

For myself, the Holy Spirit leads the Church, so when the the NT canon was formalized at the Second Council of Trullan in 692 (I didn't realize an actual council regarding this issue came so late), I can trust that. However, I trust all the councils of the (Eastern) Church.

If you don't have the same understanding of the leading of the Holy Spirit in the councils, what is the basis of authority for the NT? This is an issue that I never thought while I was Protestant, but I am sure there are many protestants who have thought about this, and so I would like to know the reasonings.