In the US:
Christianity: (78.5%)
Protestantism (51.3%)
Roman Catholicism (23.9%)
Mormonism (1.7%)
Jehovah’s Witnesses (0.7%)
Orthodox Church (0.6%)
other Christian (0.3%)
http://en.wikipedia.org/wiki/Religion_in_the_United_States
The source errantly lumps into “Protestantism” very much that did not have it’s source in Geneva.