Many of the Ivy League schools are well endowed, so they have sufficient capacity to absorb all student demand into all or nearly all majors.
However, economics appears to be capacity-limited at Cornell, since it requires grades higher than C in the prerequisites to enter: https://economics.cornell.edu/major . It may not affect frosh admission if they admit all frosh in the arts and sciences division as undeclared, but be aware of the higher grade requirements to get into the major later.