Author’s Id from wp list authors function

You can use the following:

// prepare arguments
$args  = array(
// search only for Authors role
'role' => 'Author',
// order results by display_name
'orderby' => 'display_name'
);
// Create the WP_User_Query object
$wp_user_query = new WP_User_Query($args);
// Get the results
$authors = $wp_user_query->get_results();
// Check for results
if (!empty($authors))
{
    echo '<ul>';
    // loop trough each author
    foreach ($authors as $author)
    {
        // get all the user's data
        $author_info = get_userdata($author->ID);
        echo '<li>'.$author->ID.' '.$author_info->first_name.' '.$author_info->last_name.'</li>';
    }
    echo '</ul>';
} else {
    echo 'No authors found';
}

For more reference see this.