Buying Willis Towers might enable Aon to overtake Marsh & McLennan Cos. as the world's largest brokerage by revenue.

The company has been formally exploring a sale since June, when CEO Jonathan Bush stepped down following allegations of misconduct.

Walmart and Humana have explored a wide range of options including a merger, though an outright combination isn't likely at this point, according to one source.

Aetna is preparing to meet with top U.S. Justice Department officials on Friday as it seeks to win antitrust approval for its Humana deal.

Buying Allergan, which is in Dublin, could let Pfizer relocate outside the U.S. for tax purposes, a transaction known as an inversion--and of course, Allergan has Botox and the Alzheimers drug Namenda.

Anthem is nearing an agreement to buy Cigna, sources report.

The transaction values Humana at $230 a share based on yesterdays closing price for Aetna, the companies said in a statement Friday.

The second largest U.S. health insurer Aetna appears closer to acquiring Humana and a deal could occur as early as this weekend.