“Catholics are the most populous single religion”
I dont believe that to be true
http://www.pewforum.org/2015/05/12/americas-changing-religious-landscape/
You need to look at your own figures.
There is no “protestant” church or sect. Same with “evangelical” church or sect.
There are Baptists, Episcopalians, Mormons, etc. with different beliefs except for being Christians (OK, drop the Episcopalians from that.
The largest single group with a common theology is the Catholics.