That is according to a new index compiled by Willis Towers Watson (WLTW), which ranks the 300 largest pension funds based on assets under management (AUM).

These funds saw their assets grow by 15.1% to reach $18.1trn (£14.1trn) in 2017, a significant increase on the 6.1% of growth achieved over the previous year.

The top 20 accounted for 41.1% of AUM in the ranking – up from 40.3% in 2016 – with four funds from emerging markets entering this group over the last decade.

WLTW’s global head of investment content, Roger Urwin, said emerging market funds had made a “great deal of progress” in terms of governance structures and resiliency.

“These countries are especially interesting to monitor as they are typically in the earlier stages of maturity and can continue to adapt and develop their investment models,” he added.

The top five funds for AUM are shown below (US $ millions):

The US continues to have the largest number of funds within the top 300 ranking with 133, followed by the UK on 25, Canada with 18, and Japan and Australia both on 17.

Defined contribution (DC) assets increased by 17.6% last year, while defined benefit (DB) assets grew 13.5%, and now account for 64.7% of AUM, down from 65.5% in 2016.

The share of reserve funds saw a slight increase from 11.5% to 11.8%, while hybrid funds with both DB and DC components accounted for less than 1% of the total.

“While the longer-term shift from DB to DC is widely understood and remains unchanged, it is striking that DB assets continue to grow and form the majority of the total assets,” Urwin continued.

“We see the hybrid market as an interesting area of the landscape to watch, with growth expected to continue as asset owners shift away from traditional DB strategies.”