Slav vs everything

As black, the Slav is my answer to: 1.c4, 1.d4, 1.Nf3. Is this a good idea? It seems to work reasonably well. Should I learn more about the Karo-Cann, perhaps, in order to diversify?

Checked out Danny's pawn structure 101 series yet?

http://www.chess.com/video/player/pawn-structure-101-caro-slav-1

Makes sense if you love your Slav to play the Caro against 1.e4 then.

Exactly what I need! Thank you much

And of course there's a boatload of theory on the Caro that GM Shankland covers in excruciating detail if you decide to play it.  It's saved a few correspondence games for me.

http://www.chess.com/video/player/the-complete-caro-kann---part-1-sidelines-first

Try not to watch all 9 videos in one sitting. 

Of course you can't really play the Slav against e4. The Caro and Slav are somewhat related due to a similar pawn structure, but they are fundamentally different. The Slav is significantly more active than the Caro, the Slav is considered a more active alternative to the queen's gambit declined. Comparing the Caro to the Slav is a bit like comparing the QGD to the French. 

It's much more credible to say Slav against other openings such as the English where transpositions to Slav positions are completely natural and independant lines that aren't Slav-ish are in the minority.