take it on/upon yourself to do something

take it on (oneself) to (do something)

To decide to do something even though it was not one's responsibility. I took it on myself to print out these information packets for the meeting since I knew the data might be confusing. The kids took it on themselves to wash your car—I'm so proud of them for doing it without being told!
See also: on, take
Farlex Dictionary of Idioms.

take it on/upon yourself to do something

decide to do something without asking anyone for permission: He took it upon himself to dismiss my secretary, which he had no right to do.
See also: on, something, take, upon
Farlex Partner Idioms Dictionary
See also:
  • take it on (oneself) to (do something)
  • take it upon (oneself) to (do something)
  • at (one's) expense
  • at expense
  • at somebody's expense
  • at someone's expense
  • at doorstep
  • at (one's) doorstep
  • a ball and chain
  • ball and chain