If this is an EIS shipment then it may be "normal" (I don't see any reference to Switzerland in the tracking?).
This shipment appears to have been sent via Ascendia, Usually with Ascendia I'm seeing packages going to Singapore pass through New York and then Japan before Singapore.
Since your shipment originates in Elk Groove it may take a different route.
I only use Ascendia for a few things, almost always shipments destined for Asia, for Europe I'm mostly using PostNL so most orders go to Amsterdam first and from there to the destination countries. The routing for these alternative services often take a curious route.
The customs stop in Milan is a bit unusual as is the notation "Customs retention or investigation", not much you can do except to see what the tracking shows in the next 1 - 2 days.
