promise the moon
To promise something impossible.
A politician who promises the moon during a campaign loses the voters' respect.
I can't promise you the moon, but I'll do the best job I can.
to be over the moon
Быть вне себя от счастья.
When he sent me flowers and a note, I was over the moon.
Когда он послал мне цветы и записку, я была вне себя от счастья.