The US can Court-Martial them.
or Just continue to detain them.

This ruling has so many different opinions, it will be hard to sort out the items where an actual majority ruled.

I read somewhere that Justice Kennedy, apply Geneva in total to Al Queda. That his opinion only agreed that Congressional action was lacking.

So, this is a split decision.

[LINK] Military.com The Supreme Court ruled Thursday that President Bush overstepped his authority in ordering military war crimes trials for Guantanamo Bay detainees, saying in a strong rebuke that the trials were illegal under U.S. and international …