The initial idioms of the letter U

unring	unring a bell
unseen	unsound
unstuck	unsung hero
untested waters	until all hours
until all hours (of the day and night)	until are blue in the face
until doomsday	until hell freezes over
until kingdom come	until the cows come home
until the last dog is hung	until
untimely	unto
leave no stone unturned	unvarnished truth
unwashed	unwritten law
up a blind alley	up a creek
up a storm	up a stump
up a tree	up against it
up alley	up an’ Adam