I have this and it works but it looks very messy, especially if I have over a dozen line of document.getElementById

Here's my code:

document.getElementById("a").innerHTML = "Letter a";
document.getElementById("a").innerHTML = "Letter b";
document.getElementById("a").innerHTML = "Letter c";
I can rewrite as
with (document.getElementById("a")){
   innerHTML = "Letter a";
   innerHTML = "Letter b";
   innerHTML = "Letter c";

what happen if I have this and the value that I pass in is very random.
How can I rewrite it so it will look cleaner?

document.getElementById("a1").innerHTML = "Letter a";
document.getElementById("a33").innerHTML = "Letter b";
document.getElementById("cx").innerHTML = "Letter c";
document.getElementById("dz").innerHTML = "Letter d";
document.getElementById("x99").innerHTML = "Letter e";
document.getElementById("fish").innerHTML = "Letter f";