My social security is not taxable to US as I live in Canada. How do I show that it is not taxable?

[MaryK4]

If you are a U.S. citizen or resident alien, the rules for filing income tax returns and paying estimated tax are generally the same whether you are in the United States or abroad. Your worldwide income is subject to U.S. income tax, regardless of where you reside.

[juneque]

this response is not correct.  There is a tax treaty between us and Canada that taxes social security only in canada if you are a resident of Canada.  This avoids the double taxation.