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A set of strong earnings from companies, including Caterpillar and McDonald's, lifted the Dow and drove the S&P 500 to a record high, but the tech-heavy Nasdaq was dragged lower by losses in Google parent Alphabet Inc.
Caterpillar's shares rose 4.1 percent after the company reported quarterly results that smashed expectations and raised its full-year outlook for the second time this year.
Amazon and Facebook, part of the high-flying "FANG" stocks, report results later this week, while Apple is due to report next week.
Earnings are expected to have climbed 8.8 percent in the second quarter, compared with an 8 percent rise estimated at the start of the month, according to Thomson Reuters I/B/E/S.
Advanced Micro Devices, AT&T, Chipotle and Chubb are among the major companies that report after the closing bell.
"Investors will have a lot to chew on today as earnings results include at least 12 major companies," said Peter Cardillo, chief market economist at First Standard Financial.
"We look for another mixed session as the FOMC meeting begins and the health care vote comes into play."
At 9:37 a.m. ET (1337 GMT), the Dow Jones Industrial Average was up 133.09 points, or 0.62 percent, at 21,646.26 and the S&P 500 was up 7.15 points, or 0.28 percent, at 2,477.06.
The Nasdaq Composite was down 13.74 points, or 0.21 percent, at 6,397.07.
Eight of the 11 major S&P sectors were higher, with the financial index's 1.45 percent rise leading the gainers.
The Fed kicks off a two-day meeting later in the day to discuss its monetary stance and the timing of its long-awaited balance sheet reduction.
While no rate hike is expected due to subdued inflation, the central bank's statement on Wednesday will be parsed for clues on the pace of future rate hikes.
Investors will also be keeping an eye on a Senate vote on a healthcare bill, with lawmakers voting on whether to push forward with repealing Obamacare or perhaps abandon it entirely.
DuPont was up 2.3 percent after beating estimates for profit and results.
Eli Lilly was down 3 percent, while 3M fell 4.3 percent after reporting results.
Advancing issues outnumbered decliners on the NYSE by 1,805 to 751. On the Nasdaq, 1,429 issues rose and 869 fell.