Disney doesn't break out its ESPN revenue and income, so you have to estimate it. From the WSJ:
Disney’s ESPN Reality Show Doesn’t Convince
That means ESPN is estimated to contribute about $9.5b in revenues and $3.6b in operating income to Disney in 2015.
SNL Kagan estimates that ESPN's primary channel get $6.61 per subscriber per month, and as of September of 2014, they had 95m subscribers. That more than $600m per month in revenue just from the main ESPN channel.
From their 2014 annual report:
https://cdn.thewaltdisneycompany.com/sites/default/files/reports/10k-wrap-2014_1.pdf
Just going off the prior year's numbers, ESPN alone would contribute about 19% of Disney's total revenue but nearly 28% of its operating profit. That's more than the theme parks or the movie studio segments. I would say that ESPN is one of Disney's most valuable properties.