While purchasing the first ticket, you can mark the Return button, or after purchasing one-way, you can re-enter the system and purchase the return tickets by examining the reverse route sign with the reverse route sign.
When you search for flights between Detroit and Denver, all active companies and flight times on the date you entered are listed. You can find the cheapest flight tickets by sorting this list by price.
The most frequently used airline companies from Detroit to Denver are generally
Air Canada,
KLM,
Frontier Airlines,
Delta Air Lines,
Virgin Atlantic
are companies.