Byddai cynghorau hefyd yn penderfynu sut i weithio gyda'i gilydd ar wasanaethau eraill fel gwella addysg, gwasanaethau cymdeithasol, anghenion dysgu ychwanegol, amddiffyn y cyhoedd, camddefnyddio sylweddau a hybu'r Gymraeg.
Councils would also decide how they would work together on other services like education improvement, social services, additional learning needs, public protection, substance misuse and promotion of the Welsh language.