Solid Citigroup earnings, M

US stocks scored solid gains Monday, lifted by Citigroup's better-than-expected earnings and a rash of merger and acquisition activity.

At the closing bell, the Dow Jones Industrial Average gained 111.61 points (0.66 percent) at 17,055.42.

The broad-based S&P 500 advanced 9.53 (0.48 percent) to 1,977.10, while the tech-rich Nasdaq Composite Index rose 24.93 (0.56 percent) to 4,440.42.

"After suffering through last week's dismal performance, the bulls got the trading week off on positive footing, courtesy of Citigroup's better-than-expected 2Q results, as well as a plethora of global M&A news," Charles Schwab & Co. said in a research note.

Banking giant Citigroup announced second-quarter earnings per share of $1.24, excluding a financial charge for its $7 billion settlement to settle mortgage probe claims, that was well above the $1.05 projected by analysts. Citi shares soared 3.0 percent.

Bank of America Merrill Lynch said Citi's operating performance was "encouraging for large peers that report earnings this week."

Investors apparently agreed, pushing those banks up: JPMorgan Chase (+0.9 percent), Goldman Sachs (+1.3 percent), Bank of America (+1.2 percent) and Morgan Stanley (+1.3 percent).

Dow component Boeing added 1.1 percent after announcing, at the Farnborough airshow near London, that Okay Airways, the first privately owned Chinese carrier, had agreed to buy 10 single-aisle Boeing 737 planes worth $980 million at current list prices.

US drug maker AbbVie slipped 0.2 percent after Dublin-based Shire Pharmaceuticals backed its upwardly revised $53.6 billion takeover deal and said it was close to recommending it to its shareholders. US-traded Shire shares rose 2.1 percent

AbbVie, spun off from Abbott Laboratories in 2013, had been repeatedly rejected by Shire since an initial proposal in early May.

Abbott Laboratories, meanwhile, said it was selling its branded generics drugs for developed markets to generic drugmaker Mylan for stock valued at an estimated $5.3 billion. Abbott rose 1.3 percent and Mylan gained 2.1 percent.

Online shopping site eBay and auction house Sotheby's said they were teaming up to provide an online platform for sales of art and collectibles. Shares in eBay fell 0.7 percent and Sotheby's rose 1.0 percent.

Whiting Petroleum plans to acquire Kodiak Oil & Gas in a $6 billion all-stock deal that establishes the biggest producer in the valuable Bakken/Three Forks shale region, the US companies announced. Whiting leaped 7.7 percent and Kodiak advanced 4.8 percent.

Bond prices fell. The yield on the 10-year US Treasury rose to 2.54 percent from 2.52 percent Friday, while the 30-year edged up to 3.37 percent from 3.34 percent. Bond prices and yields move inversely.