A logline that is too detailed will not work. Unnecessary details distract the reader from the main point. If the potential for conflict in the story that your logline presents can be quickly discerned, it's detailed enough. You don't even need the characters' names.
So how do you show a story's conflict potential?
A conflict is a battle between two opposing forces. Two opposing forces in a novel do not necessarily have to be two people, a good guy and a bad guy. The protagonist is usually a person or a group of people. The antagonist can be a person or a group of people OR nature, inner demons, expectations of society, etc.
The type of conflict you need to use is individual to the story. For example, in a contemporary romance, the protagonist is the hero and heroine (not one or the other), while the antagonist is whatever works against them to keep them apart. The basic concept of any romance is "will they fall in love, despite the odds, and be together at the end?"
Your premise ("concept" meaning the basic storyline you choose to build a premise on--for example, boy meets girl--and "premise" meaning the unique story you present with specific characters and a specific conflict) is then built upon the core conflict of two opposing forces.
To define your conflict, first determine how these two forces are opposing each other.
Give both the protagonist and the antagonist a goal. The easiest way to create conflict with this is to either give them the same goal, in which only one can achieve it, or make their goals direct opposites. In either situation, the potential for conflict is clear without much explanation.
A protagonist's starting goal is directly related to preserving his self-concept (more about that here). If the antagonist is a person, his goal should also be directly related to preserving his self-concept. To emphasize, consider this point from SF author Ben Bova:
There are no villains cackling and rubbing their hands in glee as they contemplate their evil deeds. There are only people with problems, struggling to solve them. Just as your protagonist is struggling to solve her problems, your antagonist is struggling to solve his. It's all a matter of viewpoint.
And to emphasize even further, here is an example:
In PITCH BLACK the goal of the protagonist (a group of marooned space travelers) is to get off the planet alive. The goal of the antagonist (carnivorous creatures native to the planet) is to feed on whatever they can find. Both goals involve survival, which is a primal need so it is easily understood. They actually have the same goal--to survive--but since the aliens want to eat the people, their goals oppose each other. This creates the conflict of the story. Just with that little bit of information above you can see the potential for conflict that can be stretched through the length of an entire plot.
It doesn't take much detail to convey a story's potential for conflict.
So what is the point of all this?
As an author, when I first start brainstorming a project, I have to find its core conflict in the basic premise before I can even write one word on one page. Without this conflict, there is no story. But it can't be just any conflict. It has to have the potential to fill a plot. You can write about a lot of "things" happening, but events alone do not make a plot. The conflict has story potential when the plot events revolve around two opposing forces each striving for a goal they feel is vital for them to achieve.
As an editor, I look for conflict potential in the author's pitch. A query letter doesn't have to be perfect for me to see this. But 9 times out of 10 (not official stats), if the author cannot define the basic conflict between protagonist and antagonist, the manuscript tends to wander without purpose. In the example of romance, the pitch must include a strong, opposing force that keeps the hero and heroine apart through the middle of the story. Without that, there is no potential for conflict.
The same is true of every story you write, any genre, any type. Without conflict, there is no story. Defining the potential for conflict in your premise is a necessary building block toward successful storytelling.