"Everything" really means "changes that I think would be better for me/the company/the world", because if you are happy with what the company is doing, you don't need to change anything.
In a truly large organization, it takes institutional knowledge to identify who will have to make a change, who maintains it long term, and who will be impacted.
Then you need to convince each group that the change you want is desirable. Sometimes this is as easy as convincing the person in charge of the group. A large one-time change is often easier than a small change to daily procedures.
As your knowledge of how the organization operates grows, so will your ability to find the necessary people and phrase things in terms of their interests. In a thousand-plus person corporation, I would expect this to take at least a year or two.
Which is why politics is always an important part of large companies. In order to get anything done you need to convince a lot of important people that it would benefit them to allow this project. Those people then consider how much they and others could leverage the project to expand their power and influence in the company, if it isn't net positive for them they probably wont agree to it.
In a truly large organization, it takes institutional knowledge to identify who will have to make a change, who maintains it long term, and who will be impacted.
Then you need to convince each group that the change you want is desirable. Sometimes this is as easy as convincing the person in charge of the group. A large one-time change is often easier than a small change to daily procedures.
As your knowledge of how the organization operates grows, so will your ability to find the necessary people and phrase things in terms of their interests. In a thousand-plus person corporation, I would expect this to take at least a year or two.