M&A has been booming in 2015, and the roughly $2 trillion in transaction volume across North American and Europe this year doesn't even factor in several announced mega-deals that have yet to close. As part of our continuing 2015 Year in Review coverage, we highlight five of the biggest announced mergers and acquisitions that dominated the headlines and will be sure to give 2016 numbers a boost—pending regulatory approval, of course.

We'll have a more detailed look at the M&A landscape with a comprehensive datagraphic next week.

For more of our year-end coverage, click here.

Pfizer-Allergan: $160 billion

Pharmaceutical giants Pfizer (NYSE: PFE) and Allergan (NYSE: AGN) announced a definitive merger agreement in November worth roughly $160 billion; the stock transaction is expected to close in 2H 2016, upon which the combined company—operating under the Pfizer name and trading under the same Pfizer ticker—would maintain Allergan's Ireland headquarters in a corporate inversion.

Anheuser Busch InBev-SABMiller: £71 billion

Following a couple months of negotiations, the world's two biggest beer companies struck a deal in November whereby Anheuser Busch InBev (NYSE: BUD) agreed to buy rival SABMiller (LON: SAB) for approximately £71 billion. The deal, which involved SABMiller divesting its interest in MillerCoors, is expected to close in the second half of 2016.

Charter Communications-Time Warner Cable: $78.7 billion

In May, U.S. cable operator Charter Communications (NASDAQ: CHTR) and Time Warner Cable (NYSE: TWC) announced a definitive merger agreement worth $78.7 billion, including debt. Charter also amended its $10 billion deal to acquire Bright House Networks, and the combination of the three companies should be a worthy rival to Comcast (NASDAQ: CMCSA), whose earlier merger agreement with Time Warner Cable was called off over regulatory concerns.

Royal Dutch Shell-BG Group: £47 billion

In a fight against plummeting oil prices, Royal Dutch Shell (NYSE: RDS.A, RDS.B) reached an agreement in April to buy BG Group (LON: BG) for about £47 billion. Expected to close in early 2016, the deal has already received antitrust approval from regulators in the U.S., Europe, Australia, China and Brazil. The combined company is expected to make a big play in the liquefied natural gas (LNG) market.

Dell-EMC: $67.1 billion

In a massive sponsor-backed transaction, Silver Lake's Dell agreed to acquire IT company EMC (NYSE: EMC) in October for roughly $67 billion—with the help of a huge debt financing package. Michael S. Dell, MSD Partners (the Dell family office) and Singapore-based Temasek also agreed to kick in equity for the deal, which is expected to close in mid-2016 if it clears all the necessary hurdles.