DTW has two showers, one regular size and one oversize to accommodate handicapped travelers. You ask for access at the main SC service counter, not the entrance reception desk downstairs. This is the club right in the midpoint of the A concourse at the corner of the walkway to the main terminal. There might be lineups in the morning when the west coast redeyes get in.

The water is warm to hot but not hot enough to do any steaming to freshen up clothing. It is the same hot water system for the hand washing water which is set lower to prevent scalding.
It is great for freshing up after my TPAC flight in from NRT before connections home.

If a clean pressed shirt is important just bring a shirt that came back from the cleaners.

I freshen up and put on a clean shirt after my TPAC to NRT before heading into town or onward to other Asian destinations. I have shirt folded from the cleaners and roll up my suit/jacket/pants in my carry-on roller.

They used to have complimentary amenities kit but none since three years ago. The only supplies are shower gels and shampoo in wall mounted dispensers. Bring your own shaving supplies.

Tip - There is usually one fresh towel on the counter for you. If you need more look in the closet.