Norway's $1 trillion sovereign wealth fund, the world's largest, doubled its return on investment in 2017, beating its benchmark.

Strong global stock markets boosted the value of the portfolio, the fund said. 

It earned a return of 13.7% in 2017, up from 6.9% in 2016. 

"The fund's cumulative return since inception has passed 4,000 billion Norwegian crowns ($511 billion). One out of four crowns of return was generated in 2017, after a very strong year for the fund," CEO Yngve Slyngstad said in a statement. 

"Again, our equity investments returned strongest with a return close to 20%," he said. 

The fund invests the proceeds from Norway's oil and gas production for future generations in stocks, bonds and property abroad. 

It is one of the world's largest shareholders, with investments in around 9,100 companies worldwide, equivalent to 1.4% of listed companies globally. 

The fund's biggest single company investment at the end of 2017 was in Apple, worth 66 billion crowns, ahead of Nestle at 51 billion and Royal Dutch Shell at 50 billion. 

Apple was also the biggest single contributor to the fund's returns in 2017, ahead of Chinese tech group Tencent Holdings and Microsoft. 

The fund's size is equivalent to $200,000 for every Norwegian man, woman and child. 

The government withdrew 61 billion Norwegian crowns during 2017 to pay for public expenses, compared with 101 billion crowns in 2016. 

CEO Yngve Slyngstad earned an annual salary of 6.7 million crowns. 

His chief investment officer for equity strategies, Petter Johnsen, earned more, with 7.4 million crowns. 

By comparison, the country's prime minister, Erna Solberg, earned 1.6 million crowns.