Floaters in both eyes gradually over past decade, could it be retinal detachment?

Not likely. Retinal detachment usually occurs rapidly (hours to days) and would cause significant vision loss. Although floaters can be a harbinger sign of retinal detachment, as long as there has not been any vision changes it is unlikely that these floaters are related. You should have a dilated eye examination to be sure. See an eye doctor soon.
See EyeMD. Common symptoms associated with rd are new floaters, flashing lights, loss of peripheral vision, and decreased vision. It is possible to have an asymptomatic rd. The best way to be sure is to see in ophthalmologist and have a dilated exam done.