Most Successful Singers(EXTREAMLY SHORT)

There are several very successful Artists out there. Most don't make enough money to have a title as "Most Successful Singer," though.
You may think It would be someone like Britney Spears or Rhianna. The Most successful singer of all Time wasn't Elvis, either. You'll be really shocked by this... The most successful singer of all time is Madonna.
Yes, its Madonna.
This all started with her song, "Like a Virgin." Her career skyrocketed from there. She's released album after album after album, single after single after single.
I thought that it would be Elvis, or Britney Spears...
Britney Spears is the 3rd most successful artist, so who is the 2nd? :)