America's insurance brokers obviously like the UK.
It is the latest in a series of moves that have seen America's insurance brokers extend their reach into the UK.
Towers Watson, another major US player, happily threw in its lot with London-based Willis Group three years later in an $18bn merger.
And Arthur J Gallagher, the Illinois-based broker and the world's fourth-biggest player, has just taken on sponsorship of rugby's Premiership as it seeks to widen its brand recognition here.
The deal, which will trigger pay-outs of £100m to JLT's top management, is also the latest in a wave of takeovers in the global risk and reinsurance sector, with this year already having seen the $15.3bn takeover of XL Group (NYSE: XL - news) by Axa (Paris: FR0000120628 - news) of France and the $5.6bn takeover of Validus by AIG, the US giant.
Those deals were partly driven by the need to cut costs in an environment in which prices are falling.
Doubtless some cost savings will follow this deal. It is being suggested that up to 5% of the combined workforce could be let go and, with JLT employing 4,000 people in the UK, that could mean job losses here.
But cost-cutting is not the main factor at play here. JLT, which is 40% owned by Jardine Matheson - the conglomerate founded 186 years ago to trade in China and Hong Kong - offers Marsh & McLennan a major opportunity for expansion, since most of its insurance revenues come from around the world.
More than half of Marsh & McLennan's business, by contrast, comes from the US.
Yet risk and reinsurance is not the only reason why Marsh & McLennan wants to buy JLT.
The British company, founded 21 years ago by the merger of Jardine Insurance Brokers and Lloyd Thompson and best known to the wider public for its sponsorship of the Condor cycling team and Britain's skeleton and bobsleigh teams, also has a sizeable presence in the growing field of providing consultancy and administration services in investment, pensions and employee benefits.
Bringing together the second and fifth-largest players in the sector in the UK, the deal will make Marsh & McLennan, which already owns the resources consulting firm Mercer, the market leader by some distance.
The pensions consulting sector has mushroomed in importance during recent years with the rise of "defined contribution" or "money purchase" pensions.
As more and more workers put their retirement savings into the latter - 6.4 million Britons were members of DC schemes as of the end of 2016 - these employees generally see their money saved in the default fund offered by their employer.
This, along with rules that require pension funds to seek investment advice, has put pressure on the trustees of such schemes to ensure that workers saving for their retirement are getting a good service from the fund managers entrusted to manage that money.
It has created a ready market for consultants to advise trustees on investment strategy and which fund managers to use.
The consultants have also, over time, offered a wider array of services including administration of schemes, for instance, writing to employees regularly to tell them how much they have saved for their retirement and their projected income on retirement. Most pension schemes are happy to outsource this work to third parties.
Yet the charges levied by the sector are somewhat opaque, rousing the interest of the Financial Conduct Authority, which this time last year referred the sector to the Competition & Markets Authority for investigation.
In saying it had "serious concerns" about the sector, the FCA noted that up to £1.6tn worth of pension assets were affected by the advice of the 12 largest pension consultancy firms, but highlighted that the largest three - Aon Hewitt, Mercer and Willis Towers Watson - had market shares of "between 50-80%".
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It also noted that pension trustees had "limited ability to assess the quality of their advice or compare services".
The extent to which this merger will create a new market leader can be shown by data published by Professional Pensions magazine.
It points out that the combined 2017 revenues of Mercer and JLT Benefit Solutions came to £505.6m, getting on for four times those of Capita Employee Benefits, the next largest player in the market after the big three.
So this deal will entrench the dominance of Mercer, Willis Towers Watson and Aon Hewitt. It is just possible it may attract the interest of the CMA.