The figures highlight growth in the share of "passive" investment, even though actively-run funds still account for a majority of the AuM total.

The 500 largest asset managers collectively oversaw $93.3 trillion of wealth last year, up 15.6 per cent from the year before, with firms based in North America holding the largest chunk although their share fell slightly, figures show.

The top 20 institutions by size – such as the likes of BlackRock and Vanguard – account for more than 43 per cent of the top 500 firms’ total AuM, highlighting a high degree of concentration in this sector, according to Willis Towers Watson’s Thinking Ahead Institute.

The research shows North America-based managers represent the majority of assets (58.1 per cent), although their share fell slightly in 2017, the first fall since 2008. European managers represent 31.8 per cent of assets managed (the UK being 7.4 per cent), Japan 4.8 per cent and the rest of the world 5.2 per cent. Assets in each region grew in 2017. While the majority of total assets (77.6 per cent) are still managed actively, the share of passive assets has grown from 19.5 per cent to 22.4 per cent in the last five years. In 2017 passive assets grew 25 per cent.

A decade-long bull market in equities – although hitting headwinds this year – has encouraged the trend of holding low-fee tracker or index funds, aka “passive” funds (although industry practitioners often say they dislike the “passive” term).
 
BlackRock remains the largest asset manager in the rankings, a position it has held since 2008 and Vanguard and State Street complete the top three for the fourth successive year.