That's one of those difficult challenges many people face when trying to communicate anything upwards. It can be with a simple email or a extensive plan to move everything to an enterprise architecture.
I feel that by far, most of the executive leadership teams I've faced in my career do not want to be bogged down by the details. They want everything at a high-level that hopefully covers everything you need in a condensed version that allows them to make a critical business decision.
At the end of the day, you must understand that you are the expert. Your job is not to convey every detail from A to Z when proposing big change or big ideas to management (unless otherwise specified by them first). You just need to highlight the key components of your proposal and leave the rest of the detail to your team, who will very much need to feed off the granularity as they put the proposal into action from A to Z.