What is output file when compiling *.cu with nvcc -cuda?

When compiling a *.cu file with nvcc -cuda, it will produce a default *.cu.cpp.ii
In the doc (NVCC :: CUDA Toolkit Documentation), it just says:

.cpp.ii appended to source file name, as in x.cu.cpp.ii. This output file can be compiled by the host compiler that was used by nvcc to preprocess the .cu file.

But it doesn’t explain what is the different between * .cu and * .cu.cpp.ii procuded. In a project i’m working, such file (*.cu.cpp.ii) can be compiled further to *.o file with clang. Does any know what such kind of file format (.cu.cpp.ii) for and why it can be compiled further with clang? Any reference and links would be helpful.