20.xx gb of "other" need help on 64gb iphone 6 plus

Soooooo I have a 64 gb iPhone 6 Plus...with a record # of 20.xx gb of "other" per iTunes. Could anyone help me to narrow down what could be using this type of space on my phone? Apps 1.XX gb, music 77 songs approx. 2 gb, pics 3000 or so 2-3 gb...but 20.xx of "other" I have no idea.