One of the easiest ways to see the universality of Islamic doctrine is to examine a manual of Sharia law such as The Reliance of the Traveller [sic]. The topics include (but are not limited to) theology, how to pray, funerals, taxes, business law, banking law, wills, marriage, how to be a wife/husband, how to be a mother/father, sex, divorce, criminal law, apostasy, political rule over the Kafir, jihad, the dhimmi, Christians, Jews, punishment, family law, food, ethics, sex, art, dress, use of the bathroom, how to say hello, knock on a door, a structure of government, and on and on. There are few details of life that are not included in Islamic doctrine.
Note that laws pertaining to the Kafirs are included in the Sharia. There is no one who is not included in Islamic doctrine. No one can opt out of the totalitarian Sharia.