Press Release – Aon NZ New Zealands leading insurance broker Aon has launched a new service that enables construction contractors to free up funds that would normally be retained in trust during commercial projects. Traditionally, retention money withheld under commercial … New Zealand’s leading insurance broker Aon has launched a new service that enables construction contractors to free up funds that would normally be retained in trust during commercial projects. Traditionally, retention money withheld under commercial construction contracts must be held on trust in the form of cash, or other liquid assets readily converted into cash, unless a complying instrument is purchased.