So you first tried hooking on to wp_insert_post_data and could save the meta data when saving Drafts but not when publishing. Then you tried hooking on to save_post and could save meta data when publishing but not when saving Drafts.

The easiest solution would be to hook on to both.

add_action('save_post', 'save_details');
add_action('wp_insert_post_data', 'save_details');

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Edit

Both save_post and wp_insert_post_data are called at the same time and pass two parameters to callback functions. In the source, it looks like this:

do_action('save_post', $post_ID, $post);
do_action('wp_insert_post', $post_ID, $post);

Bbut your function isn’t accepting any parameters. This will make return $post_ID fail and will likely cause other issues as well.

You should have:

function save_details( $post_ID, $post ) {
    ...
}

And your hook should be:

add_action( 'save_post', 'save_details', 10, 2 );

This will pass both $post_ID and $post into your function and should make things run a bit more smoothly.