keychain won't update

isn't keychain supposed to update passwords across all devices set up with icloud? the passwords are different on my iphone and mbp. i'm logged into the same network with both. in fact, i logged into a site today after changing the password and my phone asked if i wanted to update the password, i selected "yes" but it has not updated it on the phone, never mind my mbp. i tried it several times and it won't update on the phone. haven't tried on the mbp.