BOSTON — The group trying to bring the 2024 Olympics to Boston released the most detailed look yet at its bid for the Summer Games on Monday, unveiling a $4.6 billion plan it says would create thousands of jobs and housing units, expand the city’s tax base and leave behind a vastly improved regional transit system — all with a $210 million surplus. The announcement was designed to answer critics who say the privately funded Boston 2024 has withheld details of the bid to prevent the public from assessing whether the Games could be staged, as promised, without the need for taxpayer money. Chris Dempsey, co-chairman of the No Boston Olympics group, said organizers haven’t delved into the details of a proposed insurance plan to protect taxpayer interests, including whether there’s an insurer actually willing to provide the coverage. Based off a package Chicago proposed in its ultimately unsuccessful bid for the 2016 Games, the insurance would include an umbrella policy covering a range of issues like non-payment by sponsors or cancellation, as well as individual policies for venue-building projects. Boston’s bid has stumbled since getting the initial nod from the USOC, with local opposition and low poll numbers forcing organizers to spread some venues across the state to gain political support the bid couldn’t muster inside the city.