Earnings season has begin and we're finally back to fundamentals driving the stock market. There were some big winners and some big losers, but at the end of the day, the Dow Jones Industrial Average (DJINDICES:^DJI) was up just 0.52% and the S&P 500 (SNPINDEX:^GSPC) gained 0.71%. Here's what's happened with the Dow's biggest winners of the week.

Bank of America (NYSE:BAC) was up 7% to lead the Dow and was among the big banks reporting outstanding numbers during the second quarter. Revenue rose from $22 billion to only $22.7 billion, but net income jumped 63% to $4 billion, or $0.32 per share. Trading and investment banking income was strong across banks that reported this week, and the only downside was a cautious outlook about mortgage volume going forward. Interest rates have risen rapidly in the past two months, and that will keep buyers out of the market and cut the income banks can make from mortgages. The good news is that the rest of the industry is hitting on all cylinders.

DuPont (NYSE:DD) was up 5.6% on nothing more than the revelation that hedge fund manager Nelson Peltz is building a huge position in the company. Peltz didn't say much about why he bought the stock, except that the company makes him think of paint. He's alluding to the titanium oxide DuPont makes that's a key ingredient in paint. There was speculation that he may push for a spinoff of the division, but at this point, all he's done is load up on stock.

UnitedHealth Group (NYSE:UNH) rounds out the top three, climbing 5.1% after reporting a huge rise in customers and net income. At the end of the quarter it had 89.2 million people covered, up from 76.6 million a year ago. As a result, revenue jumped 12% to $30.4 million, and net income rose to $1.44 billion, or $1.40 per share. That was well ahead of expectations and shows that Obamacare may not be the negative element some expected for health insurers.

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