How do I get a document's live URL in a macro?

{% CurrentDocument.NodeAliasPath |(identity)GlobalAdministrator%}

Will get you the current documents URL.

Brenden is correct, that macro will get the current document's NodeAliasPath perfectly. In case you want the full, absolute URL (including language prefixes if you are using them) you can use the following:

{%CurrentDocument.AbsoluteURL|(identity)GlobalAdministrator%}