XY = Table[{i, Sin[i]}, {i, -10, 10, 0.5}];

DoubleXAxisPlotExample[XY : {{_?NumberQ, _?NumberQ} ..}] :=
  Overlay[{
    ListLinePlot[XY,
     ImagePadding -> 25,
     Frame -> True,
     FrameTicks -> {{All, None}, {All, None}},
     PlotRange -> All],
    ListLinePlot[Transpose[{Range[Length[XY]], Part[XY, All, 2]}],
     ImagePadding -> 25,
     Frame -> True,
     FrameTicks -> {{All, None}, {None, All}},
     PlotRange -> All]
    }];

XY = Table[{i, 100000*Sin[i]}, {i, -10, 10, 0.5}];