By my estimate, Apple has paid out $16.6 billion to content owners. $2.5 billion to app developers and about $14 billion to music companies. The developer payments are published by Apple, the music payments are estimated based on total downloads and guesses about the split and pricing of that content (90% for the content and $1 to $1.2 average pricing over time.) There might be reason to move the music figure up or down but the difference will still be nearly a factor of 5.
The cumulative payments are shown in the following chart:
