Couldn't find these default values easily so thought I write a note here. This information is for audio for video.
Auto-Match Loudness is a feature of Adobe Premiere and can be found in the essential sounds panel. With a click of a few buttons, the program will normalize your selected audio clip to some predetermined values chosen by Adobe.
These numbers are in reference to EU R128 Broadcast loudness standards. I presume that is what Adobe premiere is using since EU R128 Dialogue loudness is standardized at -23LUFS. US TV ATSC A/85 Broadcast is the usually standard that I conform to since I work and deliver my work in the US. I would shift these numbers depending on the medium you are delivering for, for instance online delivery you might want to deliver your dialogue at -18LUFS.
Couldn't find these default values easily so here they are:
SFX: -21LUFS (+2 Relative to Dialogue)
Dialogue: -23LUFS
Music: -25LUFS (-2 Relative to Dialogue)
Ambience: -30LUFS (-7 Relative to Dialogue)
The Default value for MUSIC seems pretty low so I presume that Premiere means background music or scoring. For Music with vocals I tend to set that loudness about 4 or 5db LUFS than dialogue so that would place the loudness at -18 or -19LUFS (+4-5 Relative to Dialogue).
These are all just generalizations of course. Use your ears!