Disney has been producing content for 95 years. Most of the early stuff was cartoons and animation but it also founded Touchstone Pictures. Disney is now the largest movie studio in the world with assets like the Disney Channel, Pixar, Lucasfilm, Marvel Entertainment, the Disney Digital Network, ABC television network, Fox Studios, the ESPN sports network and Radio Disney. That's a lot of programming.
Disney is famous for retaining rights to it's major copyrighted assets and using limited release schedules to extend their profitability. There will be lots of available content for Disney+ to choose from, subject to Disney regaining streaming rights once current agreements expire. Most, if not all, of it will be family oriented in nature since Disney is divesting and downsizing it's Miramax and Touchstone studios that produce more mainstream content.
Disney spends slightly more annually on new content than Netflix though less of it goes or likely will go directly to streaming. Add that new content to Disney's 95 years of back catalog and it's easy to see why it has potential to be a huge player in the streaming market. Disney will focus exclusively on family oriented programming so it stands to dominate the family subscription market.