be someone's department
US /biː ˈsʌm.wʌnz dɪˈpɑːrt.mənt/
UK /biː ˈsʌm.wʌnz dɪˈpɑːrt.mənt/

1.
urusan seseorang, tanggung jawab seseorang
to be someone's responsibility or area of expertise
:
•
I can't help you with that; it's not my department.
Saya tidak bisa membantu Anda dengan itu; itu bukan urusan saya.
•
Handling customer complaints is her department.
Menangani keluhan pelanggan adalah urusan dia.