Amazon defines this as:
Includes annual and monthly fees associated with Amazon Prime membership, as well as audiobook, e-book, digital video, digital music, and other subscription services.
2014: $2.762 billion, 2015: $4.467 billion, 2016: $6.394 billion.
Last reported quarter 2021 Q4 it was $8.12 billion, up by 15% year-over-year from $7.06 billion. From $25.21 billion in 2020 it increased by 26% to $31.77 billion in 2021.
Source: Amazon Quarterly Results.