Get Id from a conditional INSERT

For a table like this one:

CREATE TABLE Users(
    id SERIAL PRIMARY KEY,
    name TEXT UNIQUE
);

What would be the correct one-query insert for the following operation:

Given a user name, insert a new record and return the new id. But if the name already exists, just return the id.

I am aware of the new syntax within PostgreSQL 9.5 for ON CONFLICT(column) DO UPDATE/NOTHING, but I can't figure out how, if at all, it can help, given that I need the id to be returned.

It seems that RETURNING id and ON CONFLICT do not belong together.