Assets under management at the world’s largest pension funds increased in value by 6.1% in 2016, representing a total of $15.7 trillion, according to the latest global 300 research from Willis Towers Watson.

The figures for year-end 2016 show a return to growth, following a 3.4% decline in 2015, while cumulative growth in assets since 2011 now stands at 23.4%. The top 20 funds by asset size in the research experienced a higher increase than the overall ranking, growing assets by 7.1% over the period. The research shows that the world’s top 300 pension funds together now represent 43.2% of global pension assets, rising from 42.5% in 2015, as estimated against figures from Willis Towers Watson’s Global Pensions Asset Study.

According to the research, North American funds showed the most noticeable annualized growth rate over the last five years, growing by 6.7% during the period. The U.S. continues to hold its position as the country with the largest share of pension assets across the top 300 funds, representing 38.6% spread across 134 funds.

A total of 28 new funds have entered the ranking over the last five years, with the U.S. contributing the most new funds (13) on a net basis. The U.S. has the largest number of funds within the top 300 ranking (134).

Globally, defined benefit (DB) assets increased by 5.6% in 2016, compared with 9.6% for defined contribution (DC) plans, 3.9% for reserve funds and 2.9% for hybrid funds. DB assets account for 65.5% of the disclosed total advanced utilization management, down from 65.9% in 2015, while DC assets have increased their share, rising from 21.5% in 2015 to 22.2%. Reserve funds remain relatively unchanged at 11.5% (11.7% in 2015), as do hybrid funds (0.8%, falling from 0.9% in 2015).

Among the top 20 global pension funds are the U.S. Federal Thrift Savings Plan, with $485,575,000 in assets; the California Public Employees Retirement System (CalPERS), with $306,333,000 in assets; the California State Teachers Retirement System (CalSTRS), with $193,871,000 in assets; the New York State Common Retirement Fund, with $184,461,000 in assets; the New York City Retirement Fund, with $171,574,000 in assets; the Florida State Board Retirement System, with $153,942,000 in assets; and the Texas Teachers Retirement System, with $133,321,000 in assets.

“The search for attractively priced assets at acceptable risk continues to be a driving force in shaping the fortunes of pension funds and their ability to meet respective missions and objectives,” says Steve Carlson, head of Investment, North America, Willis Towers Watson. “This is increasingly hard and reduces the shine from a year in which the largest asset owners have been able to achieve superior growth. Central to this result has been the ability of leading asset owners to adapt to the ever-changing investment environment, through improvements in governance and the ability to learn from their peers. The desire of asset owners to implement best practices and sound governance has strengthened and will be a key factor in their future success.”