Welcome to FT

... need a lot more information
- from where
- class of travel
- dates of travel
- one way or return
- duration of stay
- cash ticket or with miles (this is Flyertalk)

A ticket to LAX/SFO and then a separate ticket to DTW may be cheaper, but that has risks. Your airlines choices are limited.
Airlines USA to Australia (most from LAX) are
- United (Star Alliance)
- Qantas (OneWorld Alliance)
- Delta (Skyteam Alliance)
- Virgin Australia
- Hawaiian, via Hawaii
- Air NZ, via AKL (Star Alliance)
- Fiji Airways, via Fiji
- Air Tahiti Nui (last segments on codeshares)

And others via Asia & Middle East