Amazon recently provided a bit of granularity on their growth rates by business that helps to illustrate total size of Amazon Prime (65 million members) and the rate at which Prime subscriptions are growing.

A few points to note:

Retail products are growing at a slower rate due to law of large numbers but still accelerated in 2016.
3rd party is growing at a 40% clip and continues to be the 2nd largest revenue category.
Other which includes advertising and co-branded credit cards remains small but has exploded as Amazon has focused on providing 3rd party sellers with tools to sell more through keywords and banner ads.
Prime and AWS growth rates have slowed but remain above 40% and 50% respectively.