Get your taxes done using TurboTax

To clarify, I don't have a Roth.  Just a normal run of the mill investment account...completely funded with post-tax dollars, and having paid taxes on the dividends earned each year.  So, if I now withdraw money from that account, is it taxable?  It seems like I've already paid taxes on it and on the earning from it, but I don't want to assume.  Thanks!