http://en.wikipedia.org/wiki/Fast_track_(trade)
http://fas.org/sgp/crs/misc/RL33743.pdf <<CRS is the Congressional Research Service, a useful resource for anyone interested in policy matters
http://thehill.com/homenews/administration/195858-white-hous...
(so much for the legislative branch)
I could say the same thing about the executive branch, which persons like yourself seem to think should merely administrate the legislative will. Our constitutional design institutionalizes tension between these two branches of government, and very explicitly grants the President power to make treaties, subject to a 2/3 approval from the Senate for ratification.
Trade agreements are not exactly the same as treaties, but there is ample precedent for Congress pre-emptively authorizing the President to negotiate them. The consitutional basis for this is discussed in some detail near the start of the CRS paper linked above.
He doesn't need congressional approval -- that's exactly how the TPP has been getting negotiated this entire time -- and is exactly why it's so outstandingly bad.
Back room deals regarding IP rights (pushed hard by the MPAA, RIAA and other lobbying organizations) among many other blanketed things that the public has no knowledge of nor any say in but will ultimately be as effective as law here in the country. (so much for the legislative branch)