1000px x 1000px is always 1000px x 1000px, which will always be 1 million pixels or 1 MP...
1) It does not matter what the diameter of those pixels are for that comparison. However,
2) Now enter different diameters for pixels. If a set of pixels is twice the diameter of another, they will require a chip with 4x the area to hold the same number.
3) With the larger AREA of the chip and 2xs the diagonal, you will need a lens with 2x the focal length to get the SAME field of view with the two image systems.
(I believe concept #3 is the resolution hurdle where folks get confused.)
4) Soooo, both chips have the same resolution but different image-sensor sizes and hence require different focal lengths to get the same picture. IF you now try to "compare" the cameras using the SAME lens, the sensor with the smaller pixel diameters will be able to offer greater DETAIL, assuming the lens can accomodate it, but the resultant image will be as though you cropped the center from a chip with 4X the resolution.
Hope this helps,