The president of Chicago Theological Seminary, Susan Brooks Thistlethwaite, gives us another useful word to name what is happening in American Christianity: Post-denominational
It is clear from this Pew study that the old denominational affiliations no longer apply. The religious landscape in the U.S. is best described these days as “post-denominational.” Post-denominational means that it is far less important whether you are Methodist or Baptist, or even Catholic, than where you fall along the continuum of fundamentalist to evangelical to progressive (liberal) to secular or unaligned. While some faiths or denominations generally are more evangelical or more liberal, each tradition has a wide spectrum within it. If you are a liberal Christian in a conservative Protestant denomination, you may have more in common with a Reformed Jew than with the Christians in your own denomination.
C. S. Lewis said something similar, that, as a conservative Anglican, he has more in common with conservative Catholics and conservative Baptists, than the liberals in his own denomination. But now it appears that fidelity to any denomination is fading away, while the different degrees of conservatism and liberalism are becoming institutionalized.
But think of it: The key to your religious affiliation is really how conservative or liberal you are, not any specific theology or even a specific religion?