無話不談 [无话－谈]

Jyutping mou4 waa6 bat1 taam4
Pinyin wú huà bù tán

Definitions (CC-CEDICT)
  1. not to hold anything back (idiom)
  2. (of close friends etc) to tell each other everything
Definitions (Wiktionary)
  1. phrase, idiomatic
    for there to be nothing between two people that is not spoken, no topic that is taboo; to talk about anything and everything, symbolising a close relationship in which no secrets are kept