OMAHA, Neb. — Billionaire investor Warren Buffett's holding company disclosed a new investment in power wholesaler NRG Energy Inc. Thursday in documents filed with the Securities and Exchange Commission.

The documents offer a snapshot of Berkshire Hathaway Inc.'s $58 billion portfolio of U.S. stocks at the end of the second quarter. The filings show several changes in Berkshire's stock holdings, including the sale of a large block of its Anheuser-Busch Cos. stock and the elimination of its Trane Inc. holdings.

Berkshire also received permission to conceal the status of its investment in ConocoPhillips during this quarter, which suggests Berkshire is either adding to or selling off its investment in the oil company. At the end of March, Berkshire held 17.5 million shares of ConocoPhillips stock.

Buffett's company often asks the Securities and Exchange Commission for and receives permission to not disclose information that could hurt its trading strategy because the market likes to follow what the "Oracle of Omaha's" company does.

Berkshire officials do not typically comment on its stock investments beyond what they are legally required to disclose, and spokeswoman Jackie Wilson did not immediately respond to a message left Thursday.

The filing does not differentiate between investments Berkshire makes, investments any of its more than 60 subsidiaries make or investments Buffett himself makes.

The documents show that Berkshire held 3.2 million shares of NRG stock as of June 30. NRG, based in Princeton, N.J., owns 49 power plants with a total capacity of 24,120 megawatts.

Berkshire held significantly fewer Anheuser-Busch shares at the end of the second quarter than it did earlier this year. Berkshire had 13.8 million shares of the brewer's stock at the end of June, down from the 35.6 million shares it held in March.

Berkshire may have taken advantage of some of the increase in the price of Anheuser stock after Belgian brewer InBev SA offered to take over Anheuser in early June for $65 a share.

And Berkshire added 317,200 shares of French drug maker Sanofi Aventis to bring its stake to 3.9 million shares.

Berkshire said it held 8.9 million shares of Union Pacific Corp. stock at the end of June as a result of the stock split the railroad conducted in May.

Berkshire subsidiaries include insurance, clothing, furniture, candy companies, restaurants, natural gas and corporate jet firms. Berkshire also has major investments in such companies as Coca-Cola Co. and Wells Fargo & Co.

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