In FHIR R5, there is the addition of a 64 bit integer type.

Section  4.1.3. Integer specifies that integers are 32-bit.
I request the creation of a new type:

Integer64
The Integer type represents whole numbers in the range -2^63 to (2^63)-1.

...examples...

Note that the minus sign in the representation of a negative integer is not part of the literal, it is the unary negation operator defined as part of FHIRPath syntax.