It's a difficult question to answer. The Ivy League is a collegiate athletic conference, so historically based on sports. It's made up of 8 universities, and the most prestigious of these 8 are Harvard, Yale and Princeton (HYP).
In simple terms, HYP = Oxbridge. They all score roughly the same in international university rankings, but Oxford and Cambridge tend to rank higher than Yale and Princeton (Oxbridge top 5, Yale/Princeton top 15).
The rest of the Ivy League (Brown, Columbia, Cornell, Dartmouth, UPenn) are equivalent to the other top Russel Group unis like UCL, Imperial, LSE, Edinburgh, St Andrews, Durham.
Dartmouth is the worst of all the Ivy League (internationally ranks around 150), and if it wasn't for its name prestige, I definitely wouldn't consider it superior to any of the Russel Group unis I mentioned. But as said in one of the earlier replies, looking at target unis for US banks and comparing that to the UK gives you a better idea.