NEW YORK (Reuters) - Comcast Corp's NBCUniversal business exercised an option to sell "a substantial portion" of its stake in A&E Television Networks to joint-venture partners, a filing from the media company showed.

Comcast, which owns almost 16 percent of A&E, exercised the option on March 26 and expects the deal to close in the second half of 2012, the company said in a filing with the Securities and Exchange Commission earlier this week.

"The parties are still discussing how much of the stake will be sold," The Wall Street Journal reported, citing a person familiar with the matter.

Citigroup analyst Jason Bazinet estimated the stake's value at about $2 billion, the newspaper said citing a research report.

A&E, home to channels such as The History Channel and Lifetime, fell into Comcast's hands when it bought NBCUniversal from General Electric last year.

(Reporting By Dhanya Skariachan; Editing by Maureen Bavdek)