The Indonesian Rupiah is used across Indonesia including the main islands of Java, Kalimantan, Sumatera, Sulawesi and the thousands of islands surrounding. Indonesia is the only country which uses IDR.
The value of the Rupiah has declined over years, which means your travel wallet will likely be in the millions. Something you'll have to get used to because Indonesia relies heavily on cash, especially on the islands where you'll need cash pay for most things.