Solution:

Generation Gap

Solution:

I am on cloud 9.

Solution:

Isaac Newton

Explanation:
I + Sack(saac) + Knee(new) + Ton

Solution:

Once upon a time

Solution:

12 Angry Men

Explanation:
12 (dozen = 12)
Angry (Angry Bed)
Men

Solution:

One Night Stand.

Explanation:
Number 'One' + Knight(chess piece) + st + and(symbol &)

Solution:

Nightmare.

Explanation:
(K)night + mare (A mare is the female of a horse)

Solution:

Over My Dead Body

Solution:

Bear

Explanation:
Bone - one + ear
= B + Ear
=> Bear

Solution:

Feeling on top of the World