Add Custom Field to Woo Admin Order Details

// Add Customer ID custom field to admin order data
add_action( 'woocommerce_admin_order_data_after_order_details', 'misha_editable_order_meta_customer_id' );

function misha_editable_order_meta_customer_id( $order ){
	$user_id = $order->get_customer_id();
	$user = new WP_User( $user_id );
	$customer_id = $user->billing_customer_id;	

  ?>
    <div class="address" style="display: inline-block">
      <p<?php if( empty($customer_id) ) echo ' class="form-field form-field-wide none_set"' ?>>
        <strong>Customer ID:</strong>
        <?php echo ( !empty( $customer_id ) ) ? $customer_id : 'Not specified' ?>
      </p>
    </div>
	<?php 
}