Does enumerator used in expression have the same type as underlying type of its enum?

What is the type of enumeration constant, when it is used outside unscoped enum definition?

Consider following code:

#include <iostream>

enum modes
{
    begin = 0,
    end = 1
};

int main()
{
    std::cout << std::boolalpha
        << std::is_same<unsigned int, typename std::underlying_type<modes>::type>::value
        << std::endl;
    std::cout << sizeof(modes) << std::endl;
    std::cout << (-100 + end) << std::endl;
}

This yields on my machine:

true
4
-99

Now, if I only change the value of some other enumerator, begin to 2147483648, then my output becomes:

true
4
4294967197

Apparently, It means, that type of end has changed from int to unsigned int, even underlying type of modes is still the same (i.e. unsigned int).

Are there some special rules for integral promotions regarding enums?