World Economic Forum estimates retirement shortfalls in public pension/private pension/individual savings in 2015 at 70 trillion$, and projects nearly half a quadrillion (400 tril) shortfall in 2050, with the lion's share belonging to the US. [1, page 7] Interest rates stuck at the 0 bound (and negative real) for nearly a decade haven't helped. I foresee a bumpy ride figuring out who gets stuck with the bill.

[1] http://www3.weforum.org/docs/WEF_White_Paper_We_Will_Live_to... [PDF]