The available integer conversions depend on the integer type.
Any signed or unsigned integer can be converted to a larger signed integer. Only unsigned integers can be converted to a larger unsigned integer.
Any signed or unsigned integer can be converted into a NUMERIC or DECIMAL datatype with (precision minus scale) greater than or equal to precision required to represent the maximum value of the type of the integer. Unsigned 64-bit integers cannot be converted into numeric, as they require a numeric with precision at least 19, which is unsupported.