Before I start, I want to be clear, this process works for me. It isn't for everyone, so take it with a grain of salt.

Outlining is personal. Everyone does it different. Some writers architect the full story, some outline the plot, while others discovery write everything. Personally, I get decision paralysis when I attempt to outline everything and when I attempt to discovery write everything.

When I start an outline, I tend to be detailed with setting and plot. I flush out my world and know roughly where I want the story to go. Characters are left fairly open. I create just enough of each character to get into their head. That way, I can take the characters, plop them into the setting and situation of the plot, and see what happenes. Discovery writing characters works for me, but only if I know where they are and what they should do.

Step 1: Sticky Notes... Starting out, I tend to brainstorm on sticky notes. There is something about writing ideas manually that helps me see things better than typing them. Typically, I have a vauge idea or two to start with, and not much more. I'll write it on a sticky note and stick it to my desk. Then write something else - whatever comes to mind. I keep going until some ideas start to grow. It could be a character trait, plot point, setting, whatever. I'll rearrange them to see what, if any, ideas make sense together. I'll cross things out, throw some away, pull them from the trash, rewrite them, etc. Just an idea board type activity. Sometimes I will leave them on my deak for weeks. By the time I'm done with them, they are usually sad remnants of sticky notes.

Step 2a: Outline in Word... Word worked for me for a while. I created a template in Word that helps me straighten things out. It has custom headers that fill the Navigation panel, giving me sections. Default Word has this, I've just customized the look to something more pleasant to me. The problem is exactly what you said, things get lost. It grows fast and by the time I'm done with a full outline, it's a little much.

Step 2b: Outline in OneNote... For the most part, I have transitioned to OneNote for the majority of my outlines. I created an always expanding template. It has tabs for things like Characters, Plot, Locations, Religion, Economy, Government, Magic, Weapons, Science, etc. I copy my template and start a new Notebook for each story I write. What I'm writing determines which tabs I keep. For example, if I am writing fantasy, I typically wont include the Science tab. Each tab has a page template that is automatically used when adding a new page. My character template, for example, has a table for physical traits, motivations, character arc, internal secrets, etc. I try to put down enough so I feel like I understand the person. Going overboard is easy, but I try to keep to to just what is needed.

Step 3: Scenes... Once I have a good understanding of the story, I start figuring out what scenes I need. These are typically one or two sentences and can help with plot, character development, or just something random and awesome. "A lazy pet cat that wakes up just in time to scratch the eyes out of an intruder." I throw it in. Then, rearrange. Scenes never seem to come to me in an order that make sense. I'll prune and expand, but by the time I'm done, I know the story.

Step 4: Fill in the blanks... I go one scene at a time, not necessarily in order, and fill them in. For example, Mr. Whiskers scratches Billy the Kid. Maggy sat straight up in her bed. The door banged agaist the cabin wall. Her eyes fought to stay closed as she forced them open. She couldn't make out the silhouette in the door. The moonless night was no help. "You owe me money," a gruff voice said. "Oh shit," thought Maggie. She knew that voice. If Billy came to collect, she knew he would collect - one way or another. Billy took a step into the room. His boot was muffled by a thick layer of dust. Before he took a second step, a hissing filled the room. Mr. Whiskers sprung from the end of the bed. He landed on Billy's face and started scratching the man like he was a mouse caught in the cupboard. And so on.

Step 5: Edit it together... Once you have I have all of the scenes, i stitch them together and edit it so it flows. This is where I add transitions and such. By the end, there is a completed story. It isn't perfect. There might be some fillers, but it is about 95% done.

Step 6: Rewrite it all.... I bring up a blank Word document, set it to 14pt Times New Roman, double spaced, and rewrite literally everything. I have my last draft and this one open side by side. Since I'm reading the story as I'm writing it, I notice thinga I missed or phrases I don't like.

Again, this isn't for everyone. It is a process that works for me.