If you want your posts and pages to have different layouts, you do not need to customize each and every page/post. You will simply customize 2 layouts and then rely on layout inheritance.
In the layout selector, choose the Single layout and build the layout that you want all posts to use. Note: You can also build it as a Shared Layout and apply that to the Single layout.
Make sure you save it! Then, edit the Single » Page layout
Build the layout you want and save. Now, ALL posts will use the Single layout and all Pages will use the Single » Page layout. Easy, right?
Note: Any posts or pages you’ve customized indvidually will use that layout instead of inheriting the respective layout.