Full disclosure of assets means that you are both providing bank statements, investment statements, trust holdings, properties, etc. Both parties need a clear understanding of what the other has so that the agreement can be drafted to protect them both and not just one party. A prenup is not intended to be a body of armor for the party with the most, but is designed to make certain that if the marriage were to fail, that there are contentions in place for how to divide marital assets and decide which assets are actually marital and nonmarital.
Though it may feel like planning for the marriage to fall apart, the truth is that is actually helps people to plan their life together effectively because it brings issues to the forefront where they may have never otherwise been addressed until an argument occurs.
If a prenuptial agreement seems to be right for you, contact a family law attorney to discuss your rights and options.