(Reuters) - MetLife Inc <MET.N>, the largest U.S. life insurer, reported a quarterly profit that widely missed analysts' estimates, largely due to weaker underwriting and tax-related adjustment in two of its largest markets.

The company's shares were down 3.9 percent at $42 in after-hours trading on Wednesday.

While weaker underwriting weighed on operating earnings from the Americas, the company's decision to reduce sale of yen-denominated products and tax-related adjustments hit earnings from Japan.

MetLife's Americas business, which consists of its retail and Latin America units, is the company's biggest, followed by its Asia business that includes Japan.

The company, which plans to separate a substantial portion of its U.S. Retail business, said a review of its variable annuity business during the latest quarter led to a non-cash charge of about $2 billion.

MetLife's Chief Executive Steve Kandarian said in January the company is considering splitting off its U.S. retail business, blaming the regulatory environment.

The company in March won a major regulatory and legal battle when a federal judge struck down the U.S. government's label deeming the company "too big to fail", which the U.S. government subsequently appealed against.

The company lost $2.1 billion from its derivatives program in the latest quarter, compared with $912 million a year earlier.

The insurer uses derivatives to lower risks stemming from interest rates, currency exchange rates and equities.

The company's net income fell 94 percent to $64 million, or 6 cents per share, in the second quarter ended June 30.

Total operating earnings for the Americas fell 42 percent to $835 million, whereas operating earnings for Asia fell 39 percent to $259 million.

On an operating basis, MetLife earned 83 cents per share, falling far short of analysts' average estimate of $1.35, according to Thomson Reuters I/B/E/S.

The company's total operating revenue fell 2.3 percent to $16.96 billion.

(Reporting by Sudarshan Varadhan and Nikhil Subba in Bengaluru; Editing by Sriraj Kalluvila)