How to I use a longtabu inside \newenvironment?

I have the following newenvironment defined using tabularx

\newenvironment{factlist}{%
    \newdimen\unbaseline
    \unbaseline=\dimexpr-\baselinestretch\baselineskip\relax
    \renewcommand\item[2]{%
    \textsc{##1} & {\raggedright ##2\smallskip\\}\\[\unbaseline]}
    \tabularx{\linewidth}{rX}}
    {\endtabularx}

I use it as follows:

\begin{factlist}
\item{A}{aaaa}
\item{B}{bbbb}
...
\item{Z}{zzzz}
\end{factlist}

Trouble is, the "factlist" does not split across pages. I believe this is because tabularx does not fit across pages.

I figured that "longtabu" from the "tabu" package has the same syntax as tabularx. However, I am not able to replace \tabularx and \endtabularx with \begin{longtabu} and \end{longtabu} in newenvironment. It throws a Runaway argument exception.

I am new to Latex. It would be nice if you could help me getting this code to work.

I am open to other methods as well, since all I want to do is BE ABLE TO SPLIT THE "FACTLIST" ACROSS PAGES!