expected return in US GAAP DB pension plan

Hi all,

I didn’t quite get the difference between the expected return used under US GAAP and the DR used in IFRS!

I thought both rates are used to discount the future obligation liability and calculate the interset expense and the interest income for each periode. well it’s true for IFRS I think, but not sure that’s the same use in US GAAP, otherwise why an increase in expected return, has no impact on the periodic cost (not periodic expense, I’m aware there’s a difference btw them), and net pension liability on the B/S?

thanks guys for helping with this