 A US30bn merger between Aon PLC and Willis Towers Watson PLC which would have created the worlds largest insurance broker has collapsed after hitting a major roadblock with US regulators. The US Department of Justice DOJ filed a lawsuit in June in a bid to block the combination, originally announced in March last year, on the grounds that it would reduce competition in the market and result in higher prices, particularly in the areas of reinsurance brokering, pension and retirement planning, and private retiree multi-carrier healthcare exchanges. 