No it's for International travel as well.
When we were on our way back from Venice a woman had a very small dog that was waiting at our water taxi stop and she was taking the dog in the cabin with her..They were flying back to Seattle from Venice. It was going via some stop in the East and their onward flight was with Delta as well.
Your pet can travel with you in the cabin for a one-way fee of 125 USD/CAD* (to be collected at check-in) for travel within U.S./Canada, U.S. Virgin Islands, and Puerto Rico (200 USD/CAD/EUR* for travel outside the U.S., excluding Brazil where the fee is 75 USD/CAD/EUR*).