greenmanTake it upon oneself to

This expression means: "to take on the responsibility for something without consulting or being asked to." 

E.g

He took it upon himself to call my lawyer— Se encargó de llamar a mi abogado sin consultarme

I took it upon myself to prepare the report while you were away— Por mi propia iniciativa preparé el informe mientras estabas fuera

The NSA took it upon themselves to expand the security programme— La NSA se encargó de expandir el programa de seguridad por su cuenta (sin que se les pidiera)