According to C99 standard, long long is an integer type which is at least 64-bit wide. There are two integer 64-bit types specified: long long int and unsigned long long int
So, yes, this is the biggest integer type specified by C language standard (C99 version).
There is also long double type specified by C99. It’s an extended precision floating point numeric data type long for 80-bits on most popular x86-based platforms and implementations of C language.