Do not know if I worded that right. But was wondering what you call someone who does not believe in organized religion at all. They may go to church but never as a member or follower of any particular group.
I believe the word you are looking for is 'nondenominational', as in 'nondenominational Christian'. It refers to people who don't adhere to any of the subdivisions of Christianity, such as Lutheran, Catholic, Reformed etc.
The answer is made slightly confusing because there are now churches that refer to themselves as 'nondenominational', since they do not adhere to any of the larger groupings. However some of those churches are now grouping together, thus effectively creating a 'nondenominational' denomination. But in principle 'nondenominational' is a good description.
In What I saw in America Chrsterton used the terms undenominational and unsectarian to describe such folks and to my surprise, it is a real word.
Adj. 1. undenominational - not bound or devoted to the promotion of a particular denomination; "undenominational religious instruction" nonsectarian, unsectarian - not restricted to one sect or school or party; "religious training in a nonsectarian atmosphere"; "nonsectarian colleges"; "a wide and unsectarian interest in religion"- Bertrand Russell thefreedictionary.com