This past year, the world's largest companies, including 18 property and casualty insurance companies, saw cumulative sales decline for the first time since 2010.

In 2015, revenue for the Fortune Global 500 declined 11.5 percent, and total profit declined 11.2 percent.

A slowdown in China's once-booming economy has affected companies worldwide. In addition, sustained low oil prices have erased billions in sales for giant petroleum producers. But the strengthening of the United States dollar and its impact on global trade has had the largest impact on revenues for the world's largest companies.

Strong U.S. dollar a bad thing?

So, why does a strong dollar mean lower sales for the Global 500? First, exports for U.S. corporations — the largest group on the list, with a total of 134 companies — weakened because the surging dollar meant that their prices were higher in foreign markets. Second, sales outside the U.S. — whether by U.S. or non-U.S. multi-nationals — in foreign currencies such as euros, yen, and yuan, translated into far fewer dollars than they did last year, according to Fortune

Despite the profit declines, the world's 500 largest companies generated $27.6 trillion in revenues and $1.5 trillion in profits in 2015. Together, this year's Fortune Global 500 companies employ 67 million people worldwide and are represented by 33 countries. 

Here's how the world's largest P&C insurance companies ranked this year:

USAA insurance logo

No. 444: USAA

Revenue: $24,361 million.

Profit: $2,272 million.

CEO: Stuart Parker.

Headquarters: San Antonio, Texas.

Employees: 28,681.

Years on Global 500: 3.

Website: usaa.com.

Mapfre sailboat

Mapfre's skipper Iker Martinez, fourth right, steers to win the in-port course race during the Volvo Ocean Racing in Oeiras, outside Lisbon, Saturday, June 6, 2015. (Photo: Francisco Seco/AP Photo)

No. 434: Mapfre Group

Revenue: $24,795 million.

Profit: $786 million.

CEO: Antonio Huertas Mejias.

Headquarters: Madrid, Spain.

Employees: 38,405.

Years on Global 500: 9.

Website: mapfre.com.

Travelers insurance sign on rooftop

(AP Photo)

No. 397: Travelers Cos.

Revenue: $26,800 million.

Profit: $3439 million.

CEO: Alan D. Schnitzer.

Headquarters: New York City.

Employees: 30,900.

Years on Global 500: 13.

Website: travelers.com.

Sompo Japan

No. 388: Sompo Japan Nipponkoa Holdings

Revenue: $27,123 million.

Profit: $1,329 million.

CEO: Kengo Sakurada.

Headquarters: Tokyo.

Employees: 45,326.

Years on Global 500: 20.

Website: sompo-hd.com/en.

Talanx website

No. 289: Talanx

Revenue: $35,379 million.

Profit: $814 million.

CEO: Herbert K. Haas.

Headquarters: Hanover, Germany.

Employees: 20,334.

Years on Global 500: 3.

Website: talanx.com.

Allstate insurance sign on building

(Photo: Nati Harnik/AP Photo)

No. 283: Allstate

Revenue: $35,653 million.

Profit: $2,171 million.

CEO: Thomas J. Wilson.

Headquarters: Northbrook, Illinois.

Employees: 41,350.

Years on Global 500: 21.

Website: allstate.com.

Swiss Re sign outside buidling

(AP Photo)

No. 282: Swiss Re

Revenue: $35,714 million.

Profit: $4,597 million.

CEO: Christian Mumenthaler.

Headquarters: Zurich.

Employees: 12,797.

Years on Global 500: 22.

Website: swissre.com.

Tokio Marine Group logo

No. 261: Tokio Marine Holdings

Revenue: $38,143 million.

Profit: $2,120 million.

CEO: Tsuyoshi Nagano.

Headquarters: Tokyo.

Employees: 36,920.

Years on Global 500: 22.

Liberty Mutual Insurance logo

No. 249: Liberty Mutual Insurance Group

Revenue: $39,450 million.

Profit: $514 million.

CEO: David H. Long.

Headquarters: Boston.

Employees: 50,000.

Years on Global 500: 22.

Nationwide

No. 241: Nationwide

Revenue: $40,222 million.

Profit: $581 million.

CEO: Stephen S. Rasmussen.

Headquarters: Columbus, Ohio.

Employees: 34,032.

Years on Global 500: 22.

MS&AD Insurance Group sign

No. 231: MS&AD Insurance Group Holdings

Revenue: $41,758 million.

Profit: $1,512 million.

CEO: Yasuyoshi Karasawa.

Headquarters: Tokyo.

Employees: 40,617.

Years on Global 500: 18.

Website: ms-ad-hd.com.

The AIG logo is shown above the post where it trades, on the floor of the New York Stock Exchange

(Photo: Richard Drew/AP Photo)

No. 150: AIG

Revenue: $58,327 million.

Profit: $2,196 million.

CEO: Peter D. Hancock.

Headquarters: New York City.

Employees: 66,400.

Years on Global 500: 21.

Website: aig.com.

Zurich sign outside a building

No. 141: Zurich Insurance Group

Revenue: $60,568 million.

Profit: $1,842 million.

CEO: Mario Greco.

Headquarters: Zurich.

Employees: 54,335.

Years on Global 500: 22.

Website: zurich.com.

People's Insurance Co. of China logo

No. 119: People's Insurance Co. of China

Revenue: $64,606 million.

Profit: $3,110 million.

CEO: Wu Yan.

Headquarters: Beijing.

Employees: 172,213.

Years on Global 500: 7.

Website: picc.com.cn.

Munich Re logo

No. 106: Munich Re Group

Revenue: $69,433 million.

Profit: $3,447 million.

CEO: Nikolaus von Bomhard.

Headquarters: Munich.

Employees: 43,554.

Years on Global 500: 22.

Website: munichre.com.

State Farm sign

No. 93: State Farm Insurance Cos.

Revenue: $75,697 million.

Profit: $6,229 million.

CEO: Michael L. Tipsord.

Headquarters: Bloomington, Illinois.

Employees: 70,425.

Years on Global 500: 22.

Website: statefarm.com.

Allianz flags

(Photo: Matthias Schrader/AP Photo)

No. 34: Allianz

Revenue: $122,948 million.

Profit: $7,339 million.

CEO: Oliver Bäte.

Headquarters: Munich.

Employees: 142,459.

Years on Global 500: 22.

Website: allianz.com.

Berkshire Hathaway Inc. logo

No. 11: Berkshire Hathaway

Revenue: $210,821 million.

Profit: $24,083 million.

CEO: Warren E. Buffett.

Headquarters: Omaha, Nebraska.

Employees: 331,000.

Years on Global 500: 20.

Methodology

Companies are ranked by total revenues for their respective fiscal years ended on or before March 31, 2016. Revenue figures include consolidated subsidiaries and reported revenues from discontinued operations, but exclude excise taxes. For insurance companies, revenue includes premium and annuity income, investment income, realized capital gains or losses, and other income, but excludes deposits.

The Fortune Global 500 is the annual ranking of the largest 500 corporations worldwide as measured by total revenue, whereas the Fortune 500 is exclusively U.S. corporations.

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