Stewart had a big signing bonus coming to him so Detroit had to let him go for now. They will probably resign him at a much lower rate later unless somebody else picks him up.
I did see this on Sporting News:
Sporting News wrote:James Stewart - RB, LionsMarch 9, 11:24 a.m.Stewart's agent spoke with Denver officials recently, but it's unclear how much interest, if any, the team has in him. Stewart's agent also represents Garrison Hearst and Shawn Bryson, two other backs who might have a future with the Broncos.
Fantasy Spin: Landing in Denver would do wonders for Stewart's value, but don't hold your breath.